java8新特性-foreach&lambda

本文將了解java8新特性-foreach 循環List和Map.

Map

• java8前遍歷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());
    }

• java8后

	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");
		}
	});

list

• java8前

    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);
    }

java8

    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);

本文參考: https://www.mkyong.com/java8/java-8-foreach-examples/