ForEach Example using Java 8

In this article, we will show you how to loop a List and a Map with the new Java 8 forEach statement.

1. forEach and Map

1.1 Normal way to loop a Map.

 Map<String, Integer> items = new HashMap<>();
 items.put("A", 10);
 items.put("B", 20);
 items.put("C", 30);
 items.put("D", 40);
 items.put("E", 50);
 items.put("F", 60);

 for (Map.Entry<String, Integer> entry : items.entrySet()) {
  System.out.println("Item : " + entry.getKey() + " Count : " + entry.getValue());
 }

1.2 In Java 8, you can loop a Map with forEach + lambda expression.

 Map<String, Integer> items = new HashMap<>();
 items.put("A", 10);
 items.put("B", 20);
 items.put("C", 30);
 items.put("D", 40);
 items.put("E", 50);
 items.put("F", 60);
 
 items.forEach((k,v)->System.out.println("Item : " + k + " Count : " + v));
 
 items.forEach((k,v)->{
  System.out.println("Item : " + k + " Count : " + v);
  if("E".equals(k)){
   System.out.println("Hello E");
  }
 });

2. forEach and List

2.1 Normal for-loop to loop a List.

 List<String> items = new ArrayList<>();
 items.add("A");
 items.add("B");
 items.add("C");
 items.add("D");
 items.add("E");

 for(String item : items){
  System.out.println(item);
 }

2.2 In Java 8, you can loop a List with forEach + lambda expression or method reference.

 List<String> items = new ArrayList<>();
 items.add("A");
 items.add("B");
 items.add("C");
 items.add("D");
 items.add("E");

 //lambda
 //Output : A,B,C,D,E
 items.forEach(item->System.out.println(item));
  
 //Output : C
 items.forEach(item->{
  if("C".equals(item)){
   System.out.println(item);
  }
 });
  
 //method reference
 //Output : A,B,C,D,E
 items.forEach(System.out::println);
 
 //Stream and filter
 //Output : B
 items.stream()
  .filter(s->s.contains("B"))
  .forEach(System.out::println);

References

1. Java 8 Iterable forEach JavaDoc
2. Java 8 forEach JavaDoc