The lambdas-and-streams-best-practices from namvdo

Lambdas and Streams best-practices

Lambda and Stream best practices extracted from the Modern Java in Action - Lambda, streams, functional and reactive programming and some others. Also, this repo includes some tips when using lambda and streams as a Java developer.

What are lambdas and streams?

List of (non exhautive) intermediate operations of Stream:

Operation	Type	Return Type	Argument of the Operation	Function descriptor
`filter`	Intermediate	`Stream<T>`	`Predicate<T>`	`T -> boolean`
`map`	Intermediate	`Stream<R>`	`Function<T, R>`	`T -> R`
`limit`	Intermediate	`Stream<T>`	`long`
`distinct`	Intermediate	`Stream<T>`

List of (non exhautive) terminal operations of Stream:

Operation	Type	Return Type	Purpose
`forEach`	Terminal	`void`	Consumes each element from a stream and applies a lambda to each of them.
`count`	Terminal	`long`	Returns the number of elements in a stream.
`collect`	Terminal	`Stream<T>`	Returns a collection from a stream (such as `Map`, `List` or event `Integer`).

Get the name of all dishes with calories greater than 300

Stop doing this:

List<String> highCaloricDishes = new ArrayList<>();
Iterator<String> iterator = menu.iterator();
while(iterator.hasNext()) {
  Dish dish = iterator.next();
  if(dish.getCalories() > 300) {
    highCaloricDishes.add(d.getName());
  }
}

Do this:

List<String> highCaloricDish =
  menu.stream()
  .filter(dish -> dish.getCalories() > 300)
  .collect(toList());

Print all the dishes in the collection

Stop doing this:

Iterator<String> iterator = menu.iterator();
while (iterator.hasNext()) {
  Dish dish = iterator.next();
  System.out.println(dish);
}

Do this:

menu.forEach(System.out::println);

Count the number of distinct dishes (at most 3)

Stop doing this:

Set<Dish> dishes = new HashSet<>();
int count = 0;
for(Dish dish : menu) {
   if (dish.getCalories() > 300) {
      dishes.add(dish);
      count++;
   }
   if (count == 3) break;
}

Do this:

long count = menu.stream()
  .filter(dish -> dish.getCalories() > 300)
  .distinct()
  .limit(3)
  .count();

Get vegetarian dishes from all available dishes

Stop doing this:

List<Dish> vegetarianDishes = new ArrayList<>();
for(Dish d: menu) {
  if(d.isVegetarian()){
  vegetarianDishes.add(d);
  }
}

Do this:

List<Dish> vegetarianDishes =
  menu.stream()
  .filter(Dish::isVegetarian)
  .collect(toList());

Get all the dishes with the calories lower than 320 (presume the collection is already sorted)

Stop doing this:

List<Dish> dishesWithLowerThan320Calories = new ArrayList<>();
for(Dish dish : menu) {
   if (dish.getCalories() < 320) {
       dishesWithLowerThan320Calories.add(dish);
   }	
}

Do this:

List<Dish> slicedMenu
 	= specialMenu.stream()
 	.takeWhile(dish -> dish.getCalories() < 320)
 	.collect(toList());

Get all the dishes with the calories greater than or equal to 320 (presume the collection is already sorted)

Stop doing this:

List<Dish> dishesWithLowerThan320Calories = new ArrayList<>();
for(Dish dish : menu) {
   if (dish.getCalories() >= 320) {
       dishesWithLowerThan320Calories.add(dish);
   }	
}

Do this:

List<Dish> slicedMenu
 	= specialMenu.stream()
 	.dropWhile(dish -> dish.getCalories() < 320)
 	.collect(toList());

Get a list of the first 3 dishes having calories greater than 300

Stop doing this:

List<Dish> dishes = new ArrayList<>();
int count = 0;
for(Dish dish : menu) {
   if (dish.getCalories() > 300) {
      dishes.add(dish);
   }
   if (count == 3) {
      break;
   }
}

Do this:

List<Dish> dishes = specialMenu
  .stream()
  .filter(dish -> dish.getCalories() > 300)
  .limit(3)
  .collect(toList());

Filter dishes have calories greater than 300, skip 3 first ones and return the rest

Stop doing this:

List<Dish> dishes = new ArrayList<>();
int skipCount = 0;
for(Dish dish : menu) {
  if (dish.getCalories() > 300 && skipCount == 3) {
     dishes.add(dish);
  }
  if (skipCount < 3) {
    skipCount++; 
  }
}

Do this:

List<Dish> dishes = menu.stream()
                        .filter(dish -> dish.getCalories() > 300)
                        .skip(3)
                        .collect(Collectors.toList());

Get the first 2 meat dishes

Stop doing this:

List<Dish> dishes = new ArrayList<>();
int count = 0;
for(Dish dish : menu) {
  if (dish.getType() == Dish.Type.MEAT) {
    dishes.add(dish);
    count++;
  }
  if (count == 2) {
    break;
  }
}

Do this:

List<Dish> dishes = menu.stream()
                        .filter(dish -> dish.getType() == Dish.Type.MEAT)
                        .limit(2)
                        .collect(Collectors.toList());

Group all dishes by its type

Stop doing this:

Map<Dish.Type, List<Dish>> typeToDish = new HashMap<>();
for(Dish dish : menu) {
   List<Dish> dishes = typeToDish.get(dish.getType());
   if (dishes == null) {
      dishes = new ArrayList<>();
   }
   dishes.add(dish);
   typeToDish.put(dish.getType(), dishes);
}

Do this:

 Map<Dish.Type, List<Dish>> typeToDish = menu.stream().collect(groupingBy(Dish::getType));

namvdo / lambdas-and-streams-best-practices Goto Github PK

lambdas-and-streams-best-practices's Introduction

Lambdas and Streams best-practices

What are lambdas and streams?

List of (non exhautive) intermediate operations of Stream:

List of (non exhautive) terminal operations of Stream:

Get the name of all dishes with calories greater than 300

Stop doing this:

Do this:

Print all the dishes in the collection

Stop doing this:

Do this:

Count the number of distinct dishes (at most 3)

Stop doing this:

Do this:

Get vegetarian dishes from all available dishes

Stop doing this:

Do this:

Get all the dishes with the calories lower than 320 (presume the collection is already sorted)

Stop doing this:

Do this:

Get all the dishes with the calories greater than or equal to 320 (presume the collection is already sorted)

Stop doing this:

Do this:

Get a list of the first 3 dishes having calories greater than 300

Stop doing this:

Do this:

Filter dishes have calories greater than 300, skip 3 first ones and return the rest

Stop doing this:

Do this:

Get the first 2 meat dishes

Stop doing this:

Do this:

Group all dishes by its type

Stop doing this:

Do this:

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