Java 8 forEach examples

最新推荐文章于 2025-05-16 07:30:00 发布

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本文介绍如何使用Java8的forEach语句结合Lambda表达式遍历List和Map集合。通过具体示例展示了传统for循环与Java8新特性之间的区别，以及如何利用forEach和Lambda表达式简化代码。

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转自Java 8 forEach examples

In this article, we will show you how to loop a List and a Map with the new Java 8 forEach statement.

1. forEach and Map

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());
}

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");
    }
});

2. forEach and List

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);
}

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);