java8新特性-foreach&lambda

本文将了解java8新特性-foreach 循环List和Map.

Map

• java8前遍历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后

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);

Tops:Lambda表达式实质是度函数式接口的实现；