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:

List<String>highCaloricDishes =newArrayList<>();Iterator<String>iterator =menu.iterator();while(iterator.hasNext()) {Dishdish =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()) {Dishdish =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 =newHashSet<>();intcount =0;for(Dishdish :menu) {if (dish.getCalories() >300) {dishes.add(dish);count++;   }if (count ==3)break;}

Do this:

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

Get vegetarian dishes from all available dishes

Stop doing this:

List<Dish>vegetarianDishes =newArrayList<>();for(Dishd: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 =newArrayList<>();for(Dishdish :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 =newArrayList<>();for(Dishdish :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 =newArrayList<>();intcount =0;for(Dishdish :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 =newArrayList<>();intskipCount =0;for(Dishdish :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 =newArrayList<>();intcount =0;for(Dishdish :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 =newHashMap<>();for(Dishdish :menu) {List<Dish>dishes =typeToDish.get(dish.getType());if (dishes ==null) {dishes =newArrayList<>();   }dishes.add(dish);typeToDish.put(dish.getType(),dishes);}

Do this:

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