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());
	}

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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");
		}
	});

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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);
	}

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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);