https://revature.zoom.us/j/7841280666
Day 1
Git - https://git-scm.com/download/win Jdk1.8 - uninstall any other versions of jdk and install jdk 1.8 IntelliJ - https://www.jetbrains.com/idea/download/download-thanks.html?platform=windows&code=IIC
JDK - Java Development Kit JVM - Java Virtual machine JRE - Java runtime Environment
JDK -JVM - -JRE - used to run java applications
JRE - just run JVM
Java is platform independent, it is because of JVM
void main() { }
java is case sensitive. statements must be terminated by semi colon (;)
java - compile the code ( compiler)
- check for the syntax errors
- They will generate bytecode (Hello.java --> Hello.class)
class name must begin with upper case
HelloWorld Revature Employee Customer Product String
variables must start with a lowercase
helloWorld hello_world employeeName
methods helloWorld() displayRecord()
final variable ALL CAPS
AGE APPLY_AGE
eage empAge employeeAge
alllowercase
main method is a special method which JVM calls
15 minutes checkUserDetails() This method must be called before displaying details
packages in java benefits of packages easy accessible maintain security name conflict
two types of packages built in - java.lang,java.util, java.sql user defined
String - java.lang ( automatically imported in all java classes)
access specifiers in java
folders
import hr.*;
import hr.Salary; import hr.Tax;
===================================
hr Salary Tax
finance Company Investors
Write one method in every class and call it in main method
15 minutes
public - least access specifier , ec private - most restrictive one protected - same package and all child classes (irrespective of package) default - same package
10:00 AM EST
https://revature.zoom.us/j/96121243699?pwd=djhsQzJiMnp0VUwvcGZLMmNRb1dQQT09
QC - Quiz Coding challenge
======================= Day 2 agenda Hardware fundamentals CPU/Processor/OS Garbage Collection Stack & heap
Control Flow statements if else switch nested if else
Primitive data types
int byte short long
float double
char
boolean
put your class in file put your methods in class put your statements in methods
package day2;
public class ControlFlowDemo {
int num=10;
int age;
age = 99;
public static void main(String[] args) {
System.out.println("Hello");
}
}
WAP to check the highest number between the three.
num1=981 num2=867 num3=93
The highest number is : num1
15 minutes
Arithmetic
=
< Logical Operators Short circuit & && | ||
& &&
condi1 & condi2 & condi3
condi1 && condi2 && condi3
num1=10 num2=20
num2=10 num1=9
OUT -9
num2=9 num1=10
OUT - 9
OUT - 19
Ternary Operator. age
?:
Operators
- special method
- get called automatically whenever you create an object
- same name as the class name
- not have any return type, not even void
- it is used for initialization
- can be overloaded
public class Customer { String customerName="Ananda"; public Customer(){ customerName="Daniel"; } public void changeName(){ customerName="Andrew"; } public static void main(String args[]){ Customer cust = new Customer();
System.out.println(cust.customerName);
}
}
cust.customerName="Daniel"
Methods and parameters Order of initialization
Employee
employeeId
employeeName
Create default cons
employeeId=-1
employeeName="NA"
Paramertized cons
Employee e1 = new Employee();
System.out.println(e1.employeeId); //-1
System.out.println(e1.employeeName); //NA
Employee e2 = new Employee(181,"Opeyemi");
System.out.println(e1.employeeId); //181
System.out.println(e1.employeeName); //Opeyemi
static
Num 1 : 11 Num 2 : 19 Num 1 : 100 Num 2 : 200
package day2; //QC : static keyword in java : //Ans :The static keyword in Java is used to share the same variable or method of a given class //The static keyword belongs to the class than an instance of the class. //Real Time Scenario : count number of objects created public class StaticDemo { int num1=10; static int counter=0; static int num2=20; public void changevalue(){ num1--; num2++; } public static void changeValueAgain(){ num2++; } public static void main(String[] args) {
StaticDemo d1 = new StaticDemo();
d1.counter++;
d1.changevalue();
StaticDemo d2 = new StaticDemo();
d2.counter++;
d2.changevalue();
StaticDemo.changeValueAgain();
System.out.println("D1 num1 :"+d1.num1);
System.out.println("D1 num2 :"+d1.num2);
System.out.println("D2 num1 :"+d2.num1);
System.out.println("D2 num2 :"+d2.num2);
//9 23 9 23
System.out.println("No of objects created :"+d1.counter);
}
}
Order of initialization
static block, In main W constructor instance block Z constructor W constructor instance block Z constructor
Stack function calls primitive data types (int, double, etc.) and local and reference variables of the functions are stored
Heap
object
instance scope class scope -static/global local scope block scope
Constuctor Order of initalization Overloading instance scope class scope -static/global local scope block scope
Product
productId
productName
quantityOnHand
price
count number of objects
* Use initialzer block and static intializer block to initilize the member variables
* Create default cons to initialize productId=100, productName=Lakme,quantityOnHand=100, price=90
*Create parametrized cons to assign different product values
201, Aroma, 900, 899
202, Pendrive , 877, 99
* create one to calculate the bill for a product
int calculatePrice(Product product)
{
//create local variable total
product.quantityOnHand * product.price;
}
main()
{
Print the bill for all the products
Aroma : 809100
Total products : totalNumberOfObjects
}
Week 1 Java DevOps/SRE (AWS) QC w/Tufail - Auditors (HH/ES) Wednesday, 5/11/2022 10:30 AM EST
Review - Constructor class Employee {
public Employee(String name) {
}
public Employee() {
}
}
public class ConstructorDemo {
public static void main(String[] args) {
Employee e1 = new Employee();
//java provides default constructor in every class if no constructor is there
Employee e2 = new Employee("Daniel");
}
}
OOPS concepts **
As the name suggests, Object-Oriented Programming or OOPs refers to languages that uses objects in programming.
Object-oriented programming aims to implement real-world entities like inheritance, hiding, polymorphism etc in programming.
The main aim of OOP is to bind together the data and the functions that operate on them so that no other part of the code can access this data except that function.
Access Modifier: Defines access type of the method i.e. from where it can be accessed in your application. In Java, there 4 type of the access specifiers. public: accessible in all class in your application. protected: accessible within the package in which it is defined and in its subclass(es)(including subclasses declared outside the package) private: accessible only within the class in which it is defined. default (declared/defined without using any modifier): accessible within same class and package within which its class is defined.
The return type: The data type of the value returned by the method or void if does not return a value. Method Name: the rules for field names apply to method names as well, but the convention is a little different. Parameter list: Comma separated list of the input parameters are defined, preceded with their data type, within the enclosed parenthesis. If there are no parameters, you must use empty parentheses (). Exception list: The exceptions you expect by the method can throw, you can specify these exception(s). Method body: it is enclosed between braces. The code you need to be executed to perform your intended operations. Message Passing: Objects communicate with one another by sending and receiving information to each other. A message for an object is a request for execution of a procedure and therefore will invoke a function in the receiving object that generates the desired results. Message passing involves specifying the name of the object, the name of the function and the information to be sent.
Now with basic prerequisite to step learning 4 pillar of OOPS is as follows. Let us start with learning about the different characteristics of an Object-Oriented Programming language
Abstraction - showing only relevant information Encapsulation - hiding the irrelavant information Polymorphism - many forms . patient overloading Inheritance - Re usability , extends
OOPs Concepts are as follows:
Class Object Method and method passing Pillars of OOPS Abstraction Encapsulation Inheritance Polymorphism Compile-time polymorphism Run-time polymorphism
---Class A class is a user defined blueprint or prototype from which objects are created. It represents the set of properties or methods that are common to all objects of one type. In general, class declarations can include these components, in order:
Modifiers: A class can be public or has default access (Refer this for details). Class name: The name should begin with a initial letter (capitalized by convention). Superclass(if any): The name of the class’s parent (superclass), if any, preceded by the keyword extends. A class can only extend (subclass) one parent. Interfaces(if any): A comma-separated list of interfaces implemented by the class, if any, preceded by the keyword implements. A class can implement more than one interface. Body: The class body surrounded by braces, { }.
public class Product extends Demo implements Hello,Thanks { int productId;
public void addProduct()
{
}
}
Object is a basic unit of Object Oriented Programming and represents the real life entities. A typical Java program creates many objects, which as you know, interact by invoking methods. An object consists of:
State : It is represented by attributes of an object. It also reflects the properties of an object. Behavior : It is represented by methods of an object. It also reflects the response of an object with other objects. Identity : It gives a unique name to an object and enables one object to interact with other objects.
Method: A method is a collection of statements that perform some specific task and return result to the caller. A method can perform some specific task without returning anything. Methods allow us to reuse the code without retyping the code. In Java, every method must be part of some class which is different from languages like C, C++ and Python.
Methods are time savers and help us to reuse the code without retyping the code. Let us now discuss 4 pillars of OOPS:
Pillar 1: Abstraction
Data Abstraction is the property by virtue of which only the essential details are displayed to the user.The trivial or the non-essentials units are not displayed to the user. Ex: A car is viewed as a car rather than its individual components. Data Abstraction may also be defined as the process of identifying only the required characteristics of an object ignoring the irrelevant details. The properties and behaviours of an object differentiate it from other objects of similar type and also help in classifying/grouping the objects. Consider a real-life example of a man driving a car. The man only knows that pressing the accelerators will increase the speed of car or applying brakes will stop the car but he does not know about how on pressing the accelerator the speed is actually increasing, he does not know about the inner mechanism of the car or the implementation of accelerator, brakes etc in the car. This is what abstraction is. In java, abstraction is achieved by interfaces and abstract classes. We can achieve 100% abstraction using interfaces.
Pillar 2: Encapsulation
It is defined as the wrapping up of data under a single unit. It is the mechanism that binds together code and the data it manipulates. Another way to think about encapsulation is, it is a protective shield that prevents the data from being accessed by the code outside this shield.
Technically in encapsulation, the variables or data of a class is hidden from any other class and can be accessed only through any member function of own class in which they are declared. As in encapsulation, the data in a class is hidden from other classes, so it is also known as data-hiding. Todo--------------- Encapsulation can be achieved by Declaring all the variables in the class as private and writing public methods in the class to set and get the values of variables.
Pillar 3: Inheritence
Inheritance is an important pillar of OOP(Object Oriented Programming). It is the mechanism in java by which one class is allow to inherit the features(fields and methods) of another class.
Let us discuss some of frequent used important terminologies:
Super Class: The class whose features are inherited is known as superclass(or a base class or a parent class). Sub Class: The class that inherits the other class is known as subclass(or a derived class, extended class, or child class). The subclass can add its own fields and methods in addition to the superclass fields and methods. Reusability: Inheritance supports the concept of “reusability”, i.e. when we want to create a new class and there is already a class that includes some of the code that we want, we can derive our new class from the existing class. By doing this, we are reusing the fields and methods of the existing class.
Pillar 4: Polymorphism
It refers to the ability of OOPs programming languages to differentiate between entities with the same name efficiently. This is done by Java with the help of the signature and declaration of these entities.
Note: Polymorphism in Java are mainly of 2 types:
Overloading - Compile time polymorphism Overriding - Later today - Run time polymorphism Example
// Java program to Demonstrate Polymorphism
// This class will contain // 3 methods with same name, // yet the program will // compile & run successfully public class Sum {
// Overloaded sum().
// This sum takes two int parameters
public int sum(int x, int y)
{
return (x + y);
}
// Overloaded sum().
// This sum takes three int parameters
public int sum(int x, int y, int z)
{
return (x + y + z);
}
// Overloaded sum().
// This sum takes two double parameters
public double sum(double x, double y)
{
return (x + y);
}
// Driver code
public static void main(String args[])
{
Sum s = new Sum();
System.out.println(s.sum(10, 20));
System.out.println(s.sum(10, 20, 30));
System.out.println(s.sum(10.5, 20.5));
}
}
continous memory location
int num1,num2,num3,num4,num5;
int []num = new int[5000];
-subscript starts from 0 num[0]
int marks[] = { 23,78,91,87,65,87,87};
for(int i=0;i<5;i++) { System.out.println(marks[i]); }
for(int i=0;i<marks.length;i++) { System.out.println(marks[i]); }
String names[] = new String[5];
names[0] = "Jay"; names[1] = "Daniel"; names[2] = "Richard"; names[3] = "Tarun"; names[4] = "Ahmed";
//TODo - Please print all the names
without chaining
###Print product1 details Product Id :-1 Product Name :NotAvailable Product QOH :-1 Product Price :-1 ###Print product2 details Product Id :122 Product Name :Lakme Product QOH :100 Product Price :30 ###Print product3 details Product Id :123 Product Name :Pendrive Product QOH :0 Product Price :0 ###Print product4 details Product Id :124 Product Name :null Product QOH :99 Product Price :100
###Print product1 details Product Id :-1 Product Name :NotAvailable Product QOH :-1 Product Price :-1 ###Print product2 details Product Id :122 Product Name :Lakme Product QOH :100 Product Price :30 ###Print product3 details Product Id :123 Product Name :Pendrive Product QOH :-1 Product Price :-1 ###Print product4 details Product Id :124 Product Name :NotAvailable Product QOH :99 Product Price :100
extends
Employee super/base/parent int employeeId
PermanentEmployee extends Employee
ContractEmployee extends Employee sub/derived/child/
super
*child class can access parent class resources without creating an object
- super keyword is there to acccess super class methods and variables
Object class
//Object class is the super class for all the classes in java
* multiple inheritance is not allowed in java
extends Employee,Product
//is- a test
In any object-oriented programming language, Overriding is a feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes.
public private default protected
Public, protected,default,private public, default, protected, private public, protected, default, private public,default,protected private.
public proctected default private
- while overriding , you can increase the accessbility, you cannot decrease it
**Difference between overriding and overloading The difference between overloading is that overloading is when you change the parameters of a method while in the same class and overriding is when you change the implementation of a method in a child class
S.NO Method Overloading Method Overriding
- Method overloading is a compile-time polymorphism. Method overriding is a run-time polymorphism.
- It occurs within the class. It is performed in two classes with inheritance relationships.
- Method overloading may or may not require inheritance. Method overriding always needs inheritance.
- In method overloading, methods must have the same name and different signatures. In method overriding, methods must have the same name and same signature.
- In method overloading, the return type can or can not be the same, but we just have to change the parameter. In method overriding, the return type must be the same or co-variant.
** Can you overload static method ? Yes,
** Can you override static method ? No, we cannot override static methods, it is known as hiding.
what is a co-variant.?
constructor invocation in inheritance
SubOrder static, order static, 0,10,9,15
Order class static block SubOrder class static block Order class instance block, i = 0 Order class constructor, i = 10 SubOrder class instance block, j = 9 SubOrder class constructor, j = 15
SubOrder class static block Order class static block Order class instance block,i= 0 Order class constructor,i= 10 SubOrder class instance block,j= 9 SubOrder class constructor,j= 15
Order class static block --> Order class instance block --> Order class constructor -->Suborder class static block --> Suborder class instance block --> Suborder class constructor
Order class static block Suborder class static block Order class instance block, i=0 Order class constructor, i=10 Suborder class instance block, j=9 Suborder class constructor, j=15
=======
Order class static block SubOrder class static block Order class instance block,i= 0 Order class constructor,i= 10 SubOrder class instance block,j= 9 SubOrder class constructor,j= 15
================================================================= Method overloading and overiding **
Abstract class Interface
What is constructor ? What are the OOPS concepts? What is inheritance ? What is static keyword in java ? What is default constructor ? What is overriding? Rules for overriding ? super and this keyword ? Difference between overriding and overloading ?
=============Method and Parameters void any primivite or any object public
=
Day4 Agenda
ABSTRACTION
-
OOPS - Abstract class is a class which contains abstract method.
*Cannot create an object of abstract class Abstract is a java modifier applicable for classes and methods in java but not for Variables.
Abstract can also inherit from an abstract class
pure abstract you cannot have non abstract method in an interface by default all the methods are abstract by default all the variables are final (constant)
***Difference between abstract class and interface
all methods are abstract in an interface Abstract class Interface
- Abstract class can have abstract and non-abstract methods. Interface can have only abstract methods. Since Java 8, it can have default and static methods also.
- Abstract class doesn't support multiple inheritance. Interface supports multiple inheritance.
- Abstract class can have final, non-final, static and non-static variables. Interface has only static and final variables.
- Abstract class can provide the implementation of interface. Interface can't provide the implementation of abstract class.
- The abstract keyword is used to declare abstract class. The interface keyword is used to declare interface.
- An abstract class can extend another Java class and implement multiple Java interfaces. An interface can extend another Java interface only.
- An abstract class can be extended using keyword "extends". An interface can be implemented using keyword "implements".
- A Java abstract class can have class members like private, protected, etc. Members of a Java interface are public by default. 9)Example: public abstract class Shape{ public abstract void draw(); } Example: public interface Drawable{ void draw(); }
class -->class extends class -> interface implements interface --> interface extends interface --> class not possible XX
class final - it cannot be inherited method final - it cannot be overridden variable final - it cannot be changed once assigned,
variable arguments Variable Arguments (Varargs) in Java is a method that takes a variable number of arguments. Variable Arguments in Java simplifies the creation of methods that need to take a variable number of arguments.
Garbage collection c - malloc free c++ - new delete java - new X
System.gc(); - request the GC to run
Eligible for GC.
finalize method()
The purpose of a finalize() method can be overridden for an object to include the cleanup code or to dispose of the system resources that can be done before the object is garbage collected
** What is the purpose of GC ? Garbage collection in Java is the process by which Java programs perform automatic memory management. Java programs compile to bytecode that can be run on a Java Virtual Machine, or JVM for short. When Java programs run on the JVM, objects are created on the heap, which is a portion of memory dedicated to the program
** Can we call the GC ? You can call Garbage Collector explicitly, but JVM decides whether to process the call or not
**String
jdk1.0 ** it is immutable (cannot be changed) --java.lang --group of characters --final class ** -- how many ways are there to create string Two ways to create string
- String name="Daniel";
- String name = new String("Richard");
** What is difference between == and equals method .
//equals - will check whether the two string values are same or not //== - will check refernce of the two strings
**List out some string methods
Exercise Objective(s): String class, String immutability
Exercise: Write class that declares the following String. “The quick brown fox jumps over the lazy dog”. Perform the following modifications to the above string using appropriate methods.
-
Print the character at the 12th index.
-
Check whether the String contains the word “is”. false -
-
Add the string “and killed it” to the existing string.
-
Check whether the String ends with the word “dogs”.
-
Check whether the String is equal to “The quick brown Fox jumps over the lazy Dog”.
-
Check whether the String is equal to “THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG”.
-
Find the length of the String.
-
Check whether the String matches to “The quick brown Fox jumps over the lazy Dog”.
-
Replace the word “The” with the word “A”.
-
Split the above string into two such that two animal names do not come together.
-
Print the animal names alone separately from the above string.
-
Print the above string in completely lower case.
-
Print the above string in completely upper case.
-
Find the index position of the character “a”.
-
Find the last index position of the character “e”.
Recommended duration: 30 Mins
Solution :
package day4;
public class StringAssignmentSolution {
public static void main(String[] args) {
String string = "The quick brown fox jumps over the lazy dog";
//print char at index 12
System.out.println(string.charAt(12));
//add string "and killed it" to existing string
String string1 = string.concat(" and killed it");
System.out.println(string1);
//check weather string is equal to "The quick brown fox jumps over the lazy Dog"
System.out.println(string.equals("The quick brown fox jumps over the lazy Dog"));
//check weather string is equal to "THE QUICK BROWN..."
System.out.println(string.equals("THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG"));
//find length of string
System.out.println(string.length());
//check weather string matches "The quick.... Dog"
System.out.println(string=="the quick brown fox jumps over the lazy Dog");
//replace word "The" with the word "A"
String string2 = string.replace("The", "A");
System.out.println(string2);
//split string into two so
String[] stringparts = string.split("j");
String string3 = stringparts[0];
String string4 = stringparts[1];
System.out.println(string3 + " - " + string4);
//print animal names alone
String string5 = string.substring(15,19);
String string6 = string.substring(39,43);
System.out.println(string5 +" - "+ string6);
//print above string in lower case
String string7 = string6.toLowerCase();
System.out.println(string7);
//print above string in upper case
String string8 = string7.toUpperCase();
System.out.println(string8);
//find index of character a
System.out.println(string.indexOf('a'));
//find index of character e
System.out.println(string.indexOf('e'));
}
}
Mutable
StringBuffer all the methods of string , replace
Length vs capacity
A string buffer or string builder's length is the number of characters it contains; its capacity is the number of character spaces that have been allocated.
================self study StringBuilder - StringTokenizer
super class for all the classes in java
finalize toString equals hashCode
wait notify
Group discussion
What is an abstract class ? Why we need it ? What is an interface ? Difference between interface and abstract class What is String and some of the methods of string ? Object class methods finalize toString equals hashCode What is GC ? What is the use of final keyword ?
12:00 PM - week1 wrap meeting https://revature.zoom.us/j/92456091980
Why we need it ? A Wrapper class is a class whose object wraps or contains primitive data types.
Need of Wrapper Classes
They convert primitive data types into objects. Objects are needed if we wish to modify the arguments passed into a method (because primitive types are passed by value).
int Integer char Character float Float
byte 1 Byte short 2 Short *int 4 Integer long 8 Long
float 4 *double 8
boolean false 1
char 2 Character
int num=65; char p = (char)num; sout(p); //A
byte b = 10; int num1 = b;
float salary=98.7;
sout(salary+2);
Boxing -AutoBoxing -Converting primitive to objects Unboxing - AutoBoxing -Converting objects to primitives
Casting -Explicit -Implicit
Wrapper
JDK1.5
Enhanced for loop AutoBoxing & AutoUnboxing
JDK1.8
Meta data information comments
Annotations are used to provide supplemental information about a program.
Annotations start with ‘@’. Annotations do not change the action of a compiled program. Annotations help to associate metadata (information) to the program elements i.e. instance variables, constructors, methods, classes, etc. Annotations are not pure comments as they can change the way a program is treated by the compiler.
Two types of annotation :
-
Builtin @Override @Deprecated .. many many @Test @Order
-
Custom annotation
package day5;
import java.lang.annotation.ElementType; import java.lang.annotation.Target;
@Target(ElementType.TYPE) public @interface Author { String authorName(); String purpose(); String dateCreated(); }
package day5; @Author(authorName = "Tufaill", purpose = "demo", dateCreated = "6/5/22") public class AnnotationDemo {
int num1;
@Deprecated
public void display(){
}
@Override
public String toString() {
return super.toString();
}
@Override
public boolean equals(Object obj) {
return super.equals(obj);
}
public static void main(String[] args) {
}
}
- java.util package
- used to take input from keyboard
package day5;
import java.util.Scanner;
public class ScannerDemo {
public static void main(String[] args) {
String name = null;
int age = 0;
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter your name :");
name = scanner.next();
System.out.println("Please enter your age :");
age = scanner.nextInt();
System.out.println("Welcome : "+name+ " and your age is :"+age);
}
}
Exercise : WAP to accept five numbers and print the sum of all the positive numbers
Enter five numbers :
12 12 -9 -7 2
Sum of all the positive numbers are : 26
(Optional) - You have entered 2 negative numbers.
Hint : Arrays, for loop, continue keyword
Exercise : WAP to accept five numbers and print the number of evens and odds and also negative numbers are not allowed.
Enter five numbers :
12 12 -9 Sorry, Cant continue , because you have entered negative value
Enter five numbers : 12 19 12 88 23
The count of even numbers are :3 The count of odd numbers are :2
Hint : Arrays, for loop, break keyword
numbers[i]%2 == 0
Install Maven -https://dlcdn.apache.org/maven/maven-3/3.8.5/binaries/apache-maven-3.8.5-bin.zip Install Postgresql -https://www.enterprisedb.com/postgresql-tutorial-resources-training?uuid=7c756686-90b4-4909-89ed-043e0705a76e&campaignId=7012J000001BfmaQAC
Deals with storing and retrieving data from files.
Input - Reading
Output -Write
java.io -Reader/Writer -CharacterStreams(Correct)
InputReader FileInputReader OutputReader FileOutputReader does not support seralization
-InputStream/OutputStream - Byte Streams(Correct)
FileInputStream FileOutputStream ObjectInput
File - java.io package
use case : listing all files in directory
Write a program that creates a new file called BatchMates.txt and store it in a directory named Batch. Also list the files or subdirectories present in the drive/directory where the directory Batch exists, stating if it is a file or directory.
package day5;
import java.io.File; import java.io.IOException;
public class FileExercise { public static void main(String[] args) throws IOException { File f1 = new File("h:\Batch\BatchMates.txt"); File f2 = new File("h:\Batch"); if(f2.exists() && f2.isDirectory()){ System.out.println("Folder batch already exists"); } else { f2.mkdir(); System.out.println("Successfully created the folder -Batch"); } System.out.println("Creating BatchMates.txt inside "+f2.getAbsolutePath()); f1.createNewFile(); } }
Enter the file name to copy : h:\home.txt
-
Not there h:\ah.txt does not exist, Hence cannot continue
-
Enter the file name to paste : h:\house.txt
Successfully copied h:\home.txt to h:\house.txt
Solution
package day5;
import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.util.Scanner;
public class ReadWriteFileSolution {
public static void main(String[] args) throws IOException {
//user to input read file and write name ?
/* Please enter the full file name of the file to be copied
h:\\ah.txt
System.exit(0);
h:\\ah.txt does not exist, Hence cannot continue
Please enter the full file name where this to be copied
h:\\jj.txt
*/
//create complete program
Scanner input = new Scanner(System.in);
//1. Asking the user to input read file name
System.out.println("Please enter the full name of the file to be copied:");
String file = input.nextLine();
File readFile = new File(file);
//2. checking the existence of the read file
if (!readFile.exists()) {
//if file is not there , then exiting
System.out.println("File does not exists, hence cannot continue");
System.exit(0);
}else{
//3. continue
System.out.println("Please enter the full name of the file to be pasted:");
String writeFileName = input.nextLine();
File writeFile = new File(writeFileName);
FileInputStream readStream = new FileInputStream(readFile); //byte stream
FileOutputStream writeStream = new FileOutputStream(writeFile);
int i = 0;
while ((i = readStream.read()) != -1) {
writeStream.write(i);
}
//closing the file
readStream.close();
writeStream.close();
System.out.println("Successfully copied");
}
}
}
BufferedInputStream It buffers the characters so that it can get the efficient reading of characters, arrays, etc.
====================== Object Seralization - is a process by which you reading and writing objects to a file.
ObjectInputStream -read ObjectOutputStream -write
Marker interfaces
What is Wrapper class in java ? What is annotation ? What is Serilization ?
10 minutes
Core Java -
Exception Hanlding Other topics
Maven
Git
AWS
JDBC
Logback
Exception handling
Three types of errors
- Syntax error
- Logical error
- Runtime errors (Exception Handling)
*Throwable
- Error
- Exception
CheckedException - checked at compile time - Exception and all its subclasses except RuntimeException UncheckedException
Solution:
try catch finally
Throwable Exception RuntimeException
throw throws -throws the exception to the caller,delegate the exception
throw - bring an exception
-sub class exception or runtimexception
JDK1.7 - try with resources - no need to close the resources explicitlty
Dependency management tool used for build process
Maven is a powerful project management tool that is based on POM (project object model). It is used for projects build, dependency and documentation.
pom.xml Project Object model XML file
-- .M2 folder local repository
mvn repository - mvnrepository central repository
TDD - Test Driven Development
Why test the code?
Open source testing framework junit - 5 - also know as jupiter
write test first
Use case : We have to create a calculator
add two numbers
Why ?
How ?
Methods stubs @BeforeAll -static @AfterAll -static
@BeforeEach @AfterEach
@Test is used to signal that the annotated method is a test method. @Test methods must not be private or static and must not return a value.
Calculator.java
package day6;
public class Calculator {
public int sum(int num1,int num2){
return num1+num2;
}
public int multiply(int num1, int num2) {
return num1*num2;
}
}
CalculatorTest.java
import day6.Calculator; import org.junit.jupiter.api.*;
import static org.junit.jupiter.api.Assertions.assertEquals;
@TestMethodOrder(value = MethodOrderer.OrderAnnotation.class) public class CalculatorTest2 {
Calculator calc;
int expected =0;
@BeforeAll
public static void beforeAll(){
System.out.println("Welcome to Calculator Test");
}
@AfterAll
public static void afterAll(){
System.out.println("Congratulations your tests completed.");
}
@BeforeEach
public void setUp(){
calc = new Calculator();
expected = 20;
System.out.println("before each");
}
@AfterEach
public void tearDown(){
calc= null;
expected =0;
System.out.println("after each");
}
@Test
@DisplayName("Testing sum with two whole numbers - 2nd")
@Order(2)
public void testCalculatorSum1(){
System.out.println("testCalculatorSum1 called");
int actual = calc.sum(10,10);
assertEquals(expected,actual);
}
@Test
@DisplayName("Testing sum with one whole number and zero - 3rd")
@Order(3)
public void testCalculatorSum2(){
System.out.println("testCalculatorSum2 called");
int actual = calc.sum(20,0);
assertEquals(expected,actual);
}
@Test
@DisplayName("Testing sum with one whole number and negative number - 1st")
@Order(1)
public void testCalculatorSum3(){
System.out.println("testCalculatorSum3 called");
int actual = calc.sum(30,-10);
assertEquals(expected,actual);
}
@Test
@DisplayName("Testing multiply with two whole numbers ")
@Order(4)
public void testCalculatormultiply1(){
System.out.println("testCalculatorMultiply1 called");
int actual = calc.multiply(10,2);
assertEquals(expected,actual);
}
}
Testing Exception ===================Hands-on Create two test cases to check the divide method.
calc.divide(40,2);
calc.divide(40,0); - ArithmeticException
15 minutes(4:55 PM EST)
Solution :
import Week2Day1.Calculator; import org.junit.jupiter.api.*;
import static org.junit.jupiter.api.Assertions.assertEquals; import static org.junit.jupiter.api.Assertions.assertThrows;
@TestMethodOrder(value = MethodOrderer.OrderAnnotation.class)
public class CalculatorTest { Calculator calc; int expected = 0;
@BeforeAll
public static void beforeAll(){
System.out.println("Welcome to the Calculator Test");
}
@AfterAll
public static void afterAll(){
System.out.println("Thank you for using Calculator Test");
}
@BeforeEach
public void setUp(){
calc = new Calculator();
expected = 20;
System.out.println("Before each");
}
@AfterEach
public void tearDown(){
calc = null;
expected = 0;
}
// Testing
@Test
@DisplayName("Subtraction Test1")
@Order(4)
public void testCalculatorDifference(){
int actual = calc.subtract(22, 2);
assertEquals(expected, actual);
}
@Test
@DisplayName("Subtraction Test2")
@Order(5)
public void testCalculatorDifference2(){
int actual = calc.subtract(40, 20);
assertEquals(expected, actual);
}
@Test
@DisplayName("Subtraction Test3")
@Order(6)
public void testCalculatorDifference3(){
int actual = calc.subtract(19, -1);
assertEquals(expected, actual);
}
@Test
@DisplayName("Addition Test1")
@Order(1)
public void testCalculator(){
int actual = calc.add(18, 2);
assertEquals(expected, actual);
}
@Test
@DisplayName("Addition Test2")
@Order(2)
public void testCalculator2(){
int actual = calc.add(22, -2);
assertEquals(expected, actual);
}
@Test
@DisplayName("Addition Test3")
@Order(3)
public void testCalculator3(){
int actual = calc.add(20, 0);
assertEquals(expected, actual);
}
@Test
@DisplayName("Multiplication Test1")
@Order(7)
public void testCalculatorMultiplyTest1(){
int actual = calc.multiply(20, 1);
assertEquals(expected, actual);
}
@Test
@DisplayName("Multiplication Test2")
@Order(8)
public void testCalculatorMultiplyTest2(){
int actual = calc.multiply(10, 2);
assertEquals(expected, actual);
}
@Test
@DisplayName("Multiplication Test3")
@Order(9)
public void testCalculatorMultiplyTest3(){
int actual = calc.multiply(5, 4);
assertEquals(expected, actual);
}
@Test
@DisplayName("Testing convert to numbers \"20\" ")
@Order(12)
public void testConvertNumbers1(){
System.out.println("testConvertNumbers1 called");
int actual = calc.convertToNumber("20");
assertEquals(expected,actual);
}
//Handle exception in junit
@Test
@DisplayName("Testing convert to numbers \"Twenty\" ")
@Order(13)
public void testConvertNumbers2(){
System.out.println("testConvertNumbers2 called");
assertThrows(NumberFormatException.class, () -> {
int actual = calc.convertToNumber("Twenty");
assertEquals(expected,actual);
});
}
@Test
@DisplayName("Division Test1")
@Order(10)
public void testCalculatorDivideTest1(){
int actual = calc.divide(40, 2);
assertEquals(expected, actual);
}
@Test
@DisplayName("Division Test2")
@Order(11)
public void testCalculatorDivideTest2(){
System.out.println("divideTest2 called");
assertThrows(ArithmeticException.class, () -> {
int actual = calc.divide(40, 0);
assertEquals(expected, actual);
});
}
}
=======================
Quiz has been assigned.
Group Discussion ?
What is exception handling ? What is try /catch and finally block ? **what is the difference between throw and throws why we need custom exception? **How to create custom exception ?
** What is junit ? How to write test in junit? List some junit annotations and usage?
. "Collections" is? 1534 QUESTION TYPE:Best Choice DON'T EVALUATE:NO STICKY:NO TAGS:Core JavaJava Collections CATEGORY:Java SCORE:1 ANSWER OPTION(S): NO TEXT CORRECT ANSWER? 1 The interface that all java collections implement
NO 2 A class filled with static methods used to manipulate collections
YES
- Which interface does not extend the Collection interface? 1535 QUESTION TYPE:Best Choice DON'T EVALUATE:NO STICKY:NO TAGS:Core JavaJava Collections CATEGORY:Java SCORE:1 ANSWER OPTION(S): NO TEXT CORRECT ANSWER? 1 List
NO 2 Set
NO 3 Queue
NO 4 Map
YES
**Details of collections later
Written Evalutaion - Quiz
Day 7
Git AWS Unix
Any questions ?
Tom,Dick, Harry,Ahmed,Elisa
Day 1 create controller Day 2 update the code in controller by Tom
git init - create en empty local repository
git config --global user.name "Tufail Ahmed"
git config --global user.email "[email protected]"
README.md - welcome file of your repository
git status
git add . -- add all the files
git commit -m "message"
git push
how can we add only one file git add bye.txt git add
Create a repository named revature and put README.md in local as well as central repo Create welcome.txt and write some message. commit the changes in local and then in central repository
equals() vs ==? equals - values true == - reference of the two objects false
String str1="Git"; String str2= new String("Git");
Branching rebase merge
git init git add . git commit -m "message" git push
README.md -
tufai@DESKTOP-09F8TAM MINGW64 /f/DMS (jayden) $ git branch daniel
tufai@DESKTOP-09F8TAM MINGW64 /f/DMS (jayden) $ git checkout daniel Switched to branch 'daniel'
tufai@DESKTOP-09F8TAM MINGW64 /f/DMS (daniel) $ git add JDBCDemo1.java
tufai@DESKTOP-09F8TAM MINGW64 /f/DMS (daniel) $ git commit -m "daniel finished his task" [daniel 935a7f3] daniel finished his task 1 file changed, 8 insertions(+) create mode 100644 JDBCDemo1.java
tufai@DESKTOP-09F8TAM MINGW64 /f/DMS (daniel) $ git push origin daniel Enumerating objects: 4, done. Counting objects: 100% (4/4), done. Delta compression using up to 4 threads Compressing objects: 100% (3/3), done. Writing objects: 100% (3/3), 459 bytes | 459.00 KiB/s, done. Total 3 (delta 1), reused 0 (delta 0), pack-reused 0 remote: Resolving deltas: 100% (1/1), completed with 1 local object. remote: remote: Create a pull request for 'daniel' on GitHub by visiting: remote: https://github.com/tufailahm/DMS/pull/new/daniel remote: To https://github.com/tufailahm/DMS.git
- [new branch] daniel -> daniel
tufai@DESKTOP-09F8TAM MINGW64 /f/DMS (daniel) ** Create four branches - java,sql,docker,jenkins and push one file in each of these branch.
**master branch will always have production ready code java - AbstractClassDemo.java
Amazon Web Services
What ?
ShoppingApp
security db
Linux/Unix DB - RDS
Virtual machine / installation
Use case : For learning UNIX, we need a linux machine. Solution : You can create EC2 instances
EC2- Ubuntu - 54.90.196.239 /keypair-downloads - 52.90.1.81 /devops2
Putty - remote servers
===================ec2 INSTANCES for windows machine
54.82.66.212 172.31.16.58
Administrator Ssz24Rm5GtHLi.8%i6y)g;h4@eVbL4k) Ssz24Rm5GtHLi.8%i6y)g;h4@eVbL4k)
Second Windows User name Administrator Password rqahBVXv3NC7)$!ds!S@wnO9hXxOh(qc
O.S most popular alongwith windows Linux
Unix File system
/
bin
dev
home
ubuntu
sql/
jenkins
etc
..
..
Absolute path - doesnt require where are you
cp
Relative Path
Unix SQL = Postgresql
54.87.50.42
users/owner group others
read write execute
U G O rwxrwxr-x
U G O -rw-rw-r--
chmod + - grant - - revoke
chmod ugo-rwx records.txt
Numberic :
4 - read 2 - write 1 - execute
chmod 000 records.txt - remove all the permissions chmod 777 records.txt - grant all the permissions to everyone chmod 745 records.txt - -rwxr--r-x
Use case : -rw--w---x
chmod 621 records.txt
--wxrw-r-x ??
chmod 365 records.txt
chmod ug+rw records.txt
User management
tufail - U daniel - G richard - O
group : (hr) - tufail,daniel
tufail:) hello.txt
/etc/passwd /etc/group
sudo useradd tufail -- Add a user
sudo passwd ahmed - change password
su tufail - switch user
whoami
sudo userdel ahmed - delete
ubuntu@ip-172-31-20-106:$ sudo groupadd software
ubuntu@ip-172-31-20-106:$ sudo useradd -g software mohammad
ubuntu@ip-172-31-20-106:$ sudo usermod -Gsoftware tufail
ubuntu@ip-172-31-20-106:$ id software
id: ‘software’: no such user
ubuntu@ip-172-31-20-106:$ id tufail
uid=1001(tufail) gid=1001(tufail) groups=1001(tufail),1002(software)
ubuntu@ip-172-31-20-106:$ id mohammad
uid=1002(mohammad) gid=1002(software) groups=1002(software)
richard daniel mohan trump
groups hr daniel mohan
software richard trump
- please remove mohan from the user list
vi pico
- programming techniques
- set of statements
Postgres
DBeaver - Universal sql commands - Great UI
https://dbeaver.io/files/dbeaver-ce-latest-x86_64-setup.exe
https://github.com/tufailahm/devops/blob/master/db_scripts.zip
Todo
**Stack & Heap
SQL *SQL Queries
Structurted Query Language
https://github.com/tufailahm/devops/blob/master/sql_ppt.zip
https://github.com/tufailahm/devops/blob/master/db_scripts.zip **sub languages ** DQL - select ** DML - insert , delete , update ** DDL - create,alter,drop,truncate ** DCL - grant, revoke ** TCL - commit, rollback , savepoint
** Joins ** Subqueries ** Set operators ** Procedures
select is a command by which retrieve the data.
select first_name as "First Name" ,salary ,manager_id from employees e ;
select * from employees e where salary > 30000 ;
--AND,OR,NOT, IN, NOT IN , NULL, BETWEEN select * from employees e where salary > 30000 ; select * from employees e where salary > 10000 and manager_id = 110 ; select * from employees e where salary > 10000 OR manager_id = 110 ; select * from employees e where salary between 10000 and 20000; select * from employees e where job_id = 'IT_PROG' --wild card % AND _ - like select * from employees e where first_name = 'A%' -- will not work because of = select * from employees e where first_name like 'A%' -- will work because of like select * from employees e where first_name like 'T%' -- will work because of like
select * from employees e where first_name like '_a%' --
select * from employees e where first_name like '%a%'
--hands on - list out all the names of employees that ends with a --??
--using or select * from employees e where job_id = 'IT_PROG' or job_id = 'AD_PRES' or job_id = 'PU_CLERK'
--using in select * from employees e where job_id in ('IT_PROG', 'AD_PRES' ,'PU_CLERK')
select * from employees e where job_id not in ('IT_PROG', 'AD_PRES' ,'PU_CLERK')
--print all the employees who have not been allocated to a manager select * from employees e where manager_id is null;
--hands on - list out all the names of employees that ends with a -- print first_name,salary of all the employees who reports to manager 103 -- print all the employees who is getting salary more than 10,000 and also works in department 60 -- print all the employees whose last name starts with L -- print all the employees (first_name,hire_date) who got hired after 25-06-05
Aggregate functions - sum,max,min,avg,count
*** Group By clause
--Find max salary in each department select department_id, max(salary) from employees;
group by clause - The SQL GROUP BY clause is used in collaboration with the SELECT statement to arrange identical data into groups. having clause - can be used only with group by and it is used to restrict the data in group by clause for aggregate functions. The HAVING clause was added to SQL because the WHERE keyword cannot be used with aggregate functions
========Joins in SQL====================
employees departments first_name , department_name
Neena Executive
Joins are used to display the data from more than one table using a join condition.
A JOIN clause is used to combine rows from two or more tables, based on a related column between them
Natural
Equi/Inner/Normal Join select first_name, salary, d.department_name , l.city from employees e join departments d on e.department_id = d.department_id join locations l on d.location_id = l.location_id;
** Difference between inner join and outer join
- Inner Join: Returns only the rows that are common in both tables.
- Outer Joins:
-
Full Outer Join: Returns all rows from both tables. -
Left Outer Join: Returns all rows from the left table plus the rows that the right table have in common. -
Right Outer Join: Returns all rows from the left table plus the rows that the right table have in common. - Self Join: A self-join is a regular join that joins a table to itself.
-
In practice, we typically use a self join to compare rows within the same table. -
To form a self-join, you specify the same table twice with different table aliases and provide the join -
predicate after the ON keyword.
*/
-- find all the information about employees select * from employees e
select * from departments d
select * from jobs
select * from locations l
select * from countries c
--WHERE -- *
select first_name as "First Name" ,salary ,manager_id from employees e ;
select * from employees e where salary > 30000 ;
--AND,OR,NOT, IN, NOT IN , NULL, BETWEEN select * from employees e where salary > 30000 ; select * from employees e where salary > 10000 and manager_id = 110 ; select * from employees e where salary > 10000 OR manager_id = 110 ; select * from employees e where salary between 10000 and 20000; select * from employees e where job_id = 'IT_PROG' --wild card % AND _ - like select * from employees e where first_name = 'A%' -- will not work because of = select * from employees e where first_name like 'A%' -- will work because of like select * from employees e where first_name like 'T%' -- will work because of like
select * from employees e where first_name like '_a%' --
select * from employees e where first_name like '%a%'
--hands on - list out all the names of employees that ends with a --??
--using or select * from employees e where job_id = 'IT_PROG' or job_id = 'AD_PRES' or job_id = 'PU_CLERK'
--using in select * from employees e where job_id in ('IT_PROG', 'AD_PRES' ,'PU_CLERK')
select * from employees e where job_id not in ('IT_PROG', 'AD_PRES' ,'PU_CLERK')
--print all the employees who have not been allocated to a manager select * from employees e where manager_id is null;
--hands on - list out all the names of employees that ends with a
--hands on - list out all the names of employees that ends with a select * from employees e where first_name like '%a'; --ends with a
-- print first_name,salary of all the employees who reports to manager 103 -- print all the employees who is getting salary more than 10,000 and also works in department 60 -- print all the employees whose last name starts with L -- print all the employees (first_name,hire_date) who got hired after 25-06-05
--print first)name and salary of employees who report to manager 103 select first_name as "First Name", salary from employees e where manager_id = 103;
--print all the employees who has salary more than 10000 and works in dept 60 select * from employees e where salary > 10000 and department_id = 60;
--print all the employees whose last name starts with L select * from employees e where last_name like 'L%';
--print all employees (first_name, hire_date) who got hired after 25-06-05 select first_name as "First Name", hire_date from employees e where hire_date >= '25-06-05';
**--distinct
select distinct department_id from employees e
select column_name, data_type, character_maximum_length, column_default, is_nullable from INFORMATION_SCHEMA.COLUMNS where table_name = 'employees'
** --sorting - order by select first_name ,salary , salary *12 AnnualSalary from employees e order by AnnualSalary desc ;
select first_name ,salary from employees e order by salary,first_name ;
select first_name ,salary from employees e order by 1;
========================= --WAQ to sort the employees based on hire date
----functions select upper('Tufail') select lower('AHMED') select substring('ahmed',2,4)
select * from employees e where lower(first_name) = 'steven'; select * from employees e where upper(first_name) = 'NEENA';
select upper(first_name) from employees e ;
========== WAQ to print like this
select *from employees e ;
STEVEN SALARY IS 24000 $US NEENA SALARY IS 17000 $US
select upper(concat(first_name,' salary is ',salary,' $us')) from employees e
select * from employees e ;
---------Date functions
select hire_date-CURRENT_DATE from employees e ;
select to_date('12/05/2009') - hire_date from employees e ;
SELECT AGE(timestamp '2001-04-10', timestamp '1957-06-13');
SELECT CURRENT_TIME;
SELECT DATEDIFF(to_date(hire_date), CURRENT_DATE) from employees e
--- To Fix
--Aggregate functions
select count(*) from employees e ;
select count(commission_pct) from employees e ;
select max(salary),min(salary),avg(salary), sum(salary) from employees e ;
select max(first_name) from employees e select min(first_name) from employees e select max(hire_date) from employees e
---WAQ to count how many unique departments are there ?
select count(distinct department_id) from employees e ;
select distinct department_id from employees e ;
--Find max salary in each department select department_id, max(salary) from employees group by department_id order by department_id
-- Count number of employees reporting to each manager select manager_id , count(employee_id) from employees e group by manager_id order by manager_id ;
--Count the number of employees working in each department select department_id , count(employee_id) from employees e group by department_id order by department_id
-- Count number of employees reporting to each manager and display only details of managers -- who are having more than 10 employees report to them --** ggregate functions are not allowed in WHERE select manager_id , count(employee_id) from employees e where count(employee_id) > 10 group by manager_id order by manager_id ;
--Solution is us having clause
select manager_id , count(employee_id) from employees e group by manager_id having count(employee_id) > 7 order by manager_id ;
----Joins select * from employees e
select * from departments d
--NATURAL JOIN
select first_name,department_name from employees e natural join departments d
select department_name, city from departments d2 natural join locations l
--using
select e.first_name ,e.employee_id ,e.salary ,d.department_name from employees e join departments d using (department_id)
--on -- List all the managers department select e.first_name ,e.employee_id ,e.salary ,d.department_name from employees e join departments d on (e.employee_id = d.manager_id)
-- WAQ to display first_name,salary ,department_name, city --Three way joins select first_name, salary, department_name, city from employees e join departments d using (department_id) join locations l using (location_id) ;
select first_name, salary, department_name, city from employees e
join departments d on e.employee_id = d.manager_id
join locations l on l.location_id = d.location_id
and (d.manager_id = 149)
order by salary desc;
--self join
self join
select * from employees e
Neena reports to Steven Bruce reports to Alexander
select employee.first_name || ' reports to ' || manager.first_name from employees employee join employees manager on manager.employee_id = employee .manager_id
---Inner Join
select first_name, salary, department_name, city from employees e join departments d on e.department_id = d.department_id join locations l on l.location_id = d.location_id //106
//employees who does not belong to any department is not showing up in inner join
//departments which does not have any employee is also not showing up in inner join
---Outer join select *from employees e where department_id is null; select *from departments d where manager_id is null;
--left select first_name, salary, department_name from employees e left outer join departments d on e.department_id = d.department_id
--right select first_name, salary, department_name from employees e right outer join departments d on e.department_id = d.department_id
--full select first_name, salary, department_name from employees e full outer join departments d on e.department_id = d.department_id
--------sub query
--who is getting better salary than Neena
select first_name from employees e where salary > 17000
select salary from employees e where first_name = 'Neena'
--subquery select first_name from employees e where salary > ( select salary from employees e where first_name = 'Neena')
--find out the name of the person who has been hired on the same date neena was hired
select first_name from employees e where hire_date = (select hire_date from employees e where first_name = 'Neena')
--: more than one row returned by a subquery used as an expression select first_name from employees e where hire_date IN (select hire_date from employees e where first_name = 'Alexander')
select * from employees e
-- GET ME THE NAME/s of the employee/s who works in same job_id as Lex select first_name from employees e where job_id in (select job_id from employees e where first_name = 'Lex')
-- get the details of the employee who is getting maximum salary select * from employees e where salary = (select max(salary) from employees e);
---SET Operators create table retired_employees as select * from employees e where employee_id in (108,109,110,111,112)
delete from employees where employee_id in (108,109);
employees not find 108,109 retured_employees not find 100 and others but common 110,111,112
select count() from employees e //107 select count() from retired_employees e //5
---union select * from employees union select * from retired_employees
---union all select * from employees union all select * from retired_employees
---insersect -- only common datas select * from employees intersect select * from retired_employees
--minus is not supported in postgres
ToDo
Person p = new Employee();
Object o = p; // Up-Casting
// Moving our reference variable UP the inheritance tree
Employee e = (Employee) o; // Down-Casting
// Moving our reference variable DOWN the inheritance tree
// Potentially dangerous
// Zoo z2 = (Zoo) o;
// The instanceof operator will return true if the object IS-A instance of the Class
// Then the down-cast would be safe
if(o instanceof Zoo) {
Zoo z2 = (Zoo) o;
}
Reference links :
- Git Cheat Sheet
- Git Basics
- Git Team Basics
- Hacker Rank
- Good source of practice. Use it often for practice.
SQL - DDL, TCL, DML
JDBC
Design Patterns - Creational - Singleton
----------Transaction Unit of work
insert into emp update salary update pf updates tax
**ACID -A transaction is a single logical unit of work that accesses and possibly modifies the contents of a database. Transactions access data using read and write operations. Atomicity - Either everything should be done or none Consistency - Isolation Durability
commit rollback savepoint
Dirty Read – A Dirty read is a situation when a transaction reads data that has not yet been committed. For example, Let’s say transaction 1 updates a row and leaves it uncommitted, meanwhile, Transaction 2 reads the updated row. If transaction 1 rolls back the change, transaction 2 will have read data that is considered never to have existed.
Non Repeatable read – Non Repeatable read occurs when a transaction reads the same row twice and gets a different value each time. For example, suppose transaction T1 reads data. Due to concurrency, another transaction T2 updates the same data and commit, Now if transaction T1 rereads the same data, it will retrieve a different value.
Phantom Read – Phantom Read occurs when two same queries are executed, but the rows retrieved by the two, are different. For example, suppose transaction T1 retrieves a set of rows that satisfy some search criteria. Now, Transaction T2 generates some new rows that match the search criteria for transaction T1. If transaction T1 re-executes the statement that reads the rows, it gets a different set of rows this time.
Based on these phenomena, The SQL standard defines four isolation levels :
Read Uncommitted – Read Uncommitted is the lowest isolation level. In this level, one transaction may read not yet committed changes made by other transactions, thereby allowing dirty reads. At this level, transactions are not isolated from each other.
Read Committed – This isolation level guarantees that any data read is committed at the moment it is read. Thus it does not allow dirty read. The transaction holds a read or write lock on the current row, and thus prevents other transactions from reading, updating, or deleting it.
Repeatable Read – This is the most restrictive isolation level. The transaction holds read locks on all rows it references and writes locks on referenced rows for update and delete actions. Since other transactions cannot read, update or delete these rows, consequently it avoids non-repeatable read.
Serializable – This is the highest isolation level. A serializable execution is guaranteed to be serializable. Serializable execution is defined to be an execution of operations in which concurrently executing transactions appears to be serially executing.
Constraints
PK FK - Referential Integrity Check default
ProductId scancode 1 1 1 2
--------Tow ways to create constraints Column Level Table level
Next QC : Week2 contents - Tue 5/17/2022 11:00 AM - 1:00 AM
--Referential Integrity
**Referential integrity refers to the relationship between tables. Because each table in a database must have a primary key, this primary key can appear in other tables because of its relationship to data within those tables. When a primary key from one table appears in another table, it is called a foreign key .
-- FK
Student studentId studentName courseId 101 Ahmed 3 102 Mohammad 190 XX
Course courseId courseName 1 Java 2 Docker 3 AWS
Movie movieId movieName directorId
Director
directorId
directorName
directorSpeciality
script1.sql
DROP TABLE IF EXISTS public.users CASCADE; -- Completely remove the users table, regardless of any rlationships -- Without the CASCADE keyword, this DROP statement would fail -- if there were any relationships that needed to be upheld -- Such as Foreign Keys
-- CASCADE operations are VERY dangerous and couble be very large scale -- DO NOT do this on ANY database that you are concerned about maintaining data on
CREATE TABLE public.users ( -- We list our columns along with their types -- Along with any constraints -- column_name DATATYPE CONSTRAINTS id SERIAL PRIMARY KEY, -- the SERIAL datatype is a type in postgres specifically -- that provides auto-incrementing for our primary keys -- This means that when inserting a new record, we can ignore -- inserting a value for the primary key, and it will be -- generated for us -- Aside from that, it is effectively just an INTEGER first_name VARCHAR (2000) NOT NULL CHECK (LENGTH(first_name) > 0), last_name VARCHAR (2000) NOT NULL CHECK (LENGTH(last_name) > 0), email VARCHAR (250) UNIQUE, age INTEGER NOT NULL DEFAULT 0 CHECK (age >= 0), supervisor INTEGER );
ALTER TABLE public.users ADD CONSTRAINT users_supervisor_fk FOREIGN KEY (supervisor) REFERENCES users (id); -- ALTER TABLE schema.table -- ADD CONSTRAINT constraint_name -- CONSTRAINT_TYPE (column) [REFERENCES table (column)]
/* This is a multi-line comment */
DROP TABLE IF EXISTS public.phonenumbers CASCADE;
CREATE TABLE public.phonenumbers ( id SERIAL PRIMARY KEY, user_id INTEGER NOT NULL REFERENCES public.users (id), home VARCHAR (20), mobile VARCHAR (20), work VARCHAR (20) );
DROP SCHEMA IF EXISTS project0 CASCADE;
CREATE SCHEMA project0;
DROP TABLE IF EXISTS public.accounts CASCADE;
CREATE TABLE accounts ( id SERIAL PRIMARY KEY, owner_id INTEGER NOT NULL REFERENCES users (id), balance NUMERIC (40, 2) NOT NULL DEFAULT 0 );
INSERT INTO public.users (first_name, last_name) VALUES ('Matthew', 'Oberlies');
SELECT first_name, last_name FROM users;
SELECT * FROM users;
-- You can construct custom columns from the columns within the tables -- The || is performing string concatenation -- Can use the AS keyword as an alias SELECT first_name || ' ' || last_name AS full_name FROM users;
INSERT INTO public.accounts (owner_id) VALUES (1);
INSERT INTO public.users (first_name, last_name) VALUES ('Jared', 'Malkin');
INSERT INTO public.accounts (owner_id, balance) VALUES (2, 3);
INSERT INTO public.users (first_name, last_name) VALUES ('Fatima', 'Melgar');
SELECT * FROM public.users INNER JOIN public.accounts ON public.users.id = public.accounts.owner_id;
SELECT first_name || ' ' || last_name AS full_name, balance FROM public.users INNER JOIN public.accounts ON public.users.id = public.accounts.owner_id;
SELECT public.accounts.id AS account_id, public.users.id AS user_id, balance FROM public.users INNER JOIN public.accounts ON public.users.id = public.accounts.owner_id;
-- You can nest SELECT statements by creating sub-queries -- This has a lot of useful use-cases -- However, you must be careful about ambiguity SELECT sub1.user_id AS user_id, sub1.balance FROM (SELECT public.accounts.id AS account_id, public.users.id AS user_id, balance FROM public.users INNER JOIN public.accounts ON public.users.id = public.accounts.owner_id) AS sub1;
SELECT * FROM ( SELECT public.accounts.id AS account_id, public.users.id AS user_id, balance FROM public.users INNER JOIN public.accounts ON public.users.id = public.accounts.owner_id) AS sub1 WHERE sub1.balance > 0;
-- WHERE -- ORDER BY -- GROUP BY -- HAVING -- LIMIT -- HAVING and WHERE are almost the exact same clause -- The difference is that WHERE applies the filter BEFORE data is grouped -- And HAVING applies the filter AFTER the data is grouped
DROP TABLE IF EXISTS one CASCADE; DROP TABLE IF EXISTS two CASCADE;
CREATE TABLE one ( one INTEGER PRIMARY KEY, two INTEGER );
CREATE TABLE two ( one INTEGER PRIMARY KEY, two INTEGER );
INSERT INTO one VALUES (1, 1), (2, 2); INSERT INTO two VALUES (1, 1), (2, 1);
-- All SET operations only operate on results that have -- the same number and type of columns
-- The UNION operator will combine all results together -- However, it will not include duplicates SELECT * FROM public.one UNION SELECT * FROM public.two;
-- UNION ALL does include duplicates SELECT * FROM public.one UNION ALL SELECT * FROM public.two;
-- INTERSECT will only include matching results SELECT * FROM public.one INTERSECT SELECT * FROM public.two;
-- EXCEPT will keep results from the left view, and remove any matching -- results that came from the right SELECT * FROM public.one EXCEPT SELECT * FROM public.two;
-- SQL supports scalar and aggregate functions that can be used -- along with SELECT statements
-- Scalar functions are functions that operate on only a single input -- and produce 1 output for each input -- e.g UPPER, LOWER, TRIM, SIN, COS, TAN
-- Aggregate functions are functions that operate on an entire column as input -- and produce 1 output for all inputs -- e.g SUM, AVG, etc
SELECT SIN(one) FROM one;
SELECT SUM(one) FROM two;
SELECT AVG(LENGTH(first_name)) FROM users;
SELECT AVG(LENGTH(last_name)) FROM users;
INSERT INTO public.users (first_name, last_name, age) VALUES ('Rubeus', 'Hagrid', 33);
SELECT age, AVG(LENGTH(first_name)) AS first_name_length_avg FROM users GROUP BY age;
-- The below query does not work, since we must either group by id OR use id in an aggregate function SELECT id, age, AVG(LENGTH(last_name)) AS last_name_length_avg FROM users GROUP BY age;
scrip1.sql
DROP TYPE IF EXISTS project0.role CASCADE; CREATE TYPE project0.role AS ENUM ('Admin', 'Employee', 'Customer');
DROP TABLE IF EXISTS project0.users CASCADE; CREATE TABLE project0.users ( id SERIAL PRIMARY KEY, username VARCHAR (250) UNIQUE NOT NULL, password VARCHAR (250) NOT NULL, role project0.ROLE NOT NULL );
DROP TABLE IF EXISTS project0.accounts CASCADE; CREATE TABLE project0.accounts ( id SERIAL PRIMARY KEY, balance NUMERIC (50, 2) NOT NULL CHECK (balance >= 0) DEFAULT 0 -- owner INTEGER NOT NULL REFERENCES project0.users (id) -- active BOOLEAN DEFAULT false );
DROP TABLE IF EXISTS project0.users_accounts_jt; CREATE TABLE project0.users_accounts_jt ( owner INTEGER NOT NULL REFERENCES project0.users (id), account INTEGER NOT NULL REFERENCES project0.accounts (id) );
DROP TABLE IF EXISTS project0.applications CASCADE; CREATE TABLE project0.applications ( id SERIAL PRIMARY KEY, owner INTEGER NOT NULL REFERENCES project0.users (id) );
INSERT INTO project0.users (username, password, role) VALUES ('moberlies', 'password', 'Admin');
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