本文将了解java8新特性-foreach 循环List和Map.

 

Map

  • java8前遍历map
 1 Map<String, Integer> items = new HashMap<>();
 2     items.put("A", 10);
 3     items.put("B", 20);
 4     items.put("C", 30);
 5     items.put("D", 40);
 6     items.put("E", 50);
 7     items.put("F", 60);
 8 
 9     for (Map.Entry<String, Integer> entry : items.entrySet()) {
10         System.out.println("Item : " + entry.getKey() + " Count : " + entry.getValue());
11     }
  • java8后
 1 Map<String, Integer> items = new HashMap<>();
 2     items.put("A", 10);
 3     items.put("B", 20);
 4     items.put("C", 30);
 5     items.put("D", 40);
 6     items.put("E", 50);
 7     items.put("F", 60);
 8     
 9     items.forEach((k,v)->System.out.println("Item : " + k + " Count : " + v));
10     
11     items.forEach((k,v)->{
12         System.out.println("Item : " + k + " Count : " + v);
13         if("E".equals(k)){
14             System.out.println("Hello E");
15         }
16     });

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；