Java 8 forEach examples遍历例子

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()); } 

Copy

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"); } }); 

Copy

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); } 

Copy

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);