Java8中Map的遍历方式总结详解编程语言

public class LambdaMap { 
 
    private Map<String, Object> map = new HashMap<>(); 
 
    @Before 
    public void initData() { 
        map.put("key1", "value1"); 
        map.put("key2", "value2"); 
        map.put("key3", "value3"); 
        map.put("key4", 4); 
        map.put("key5", 5); 
        map.put("key5", 'h'); 
    } 
 
 
    /** 
     * 遍历Map的方式一 
     * 通过Map.keySet遍历key和value 
     */ 
    @Test 
    public void testErgodicWayOne() { 
        System.out.println("---------------------Before JAVA8 ------------------------------"); 
        for (String key : map.keySet()) { 
            System.out.println("map.get(" + key + ") = " + map.get(key)); 
        } 
        System.out.println("---------------------JAVA8 ------------------------------"); 
        map.keySet().forEach(key -> System.out.println("map.get(" + key + ") = " + map.get(key))); 
    } 
 
    /** 
     * 遍历Map第二种 
     * 通过Map.entrySet使用Iterator遍历key和value 
     */ 
    @Test 
    public void testErgodicWayTwo() { 
        System.out.println("---------------------Before JAVA8 ------------------------------"); 
        Iterator<Map.Entry<String, Object>> iterator = map.entrySet().iterator(); 
        while (iterator.hasNext()) { 
            Map.Entry<String, Object> entry = iterator.next(); 
            System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue()); 
        } 
        System.out.println("---------------------JAVA8 ------------------------------"); 
        map.entrySet().iterator().forEachRemaining(item -> System.out.println("key:value=" + item.getKey() + ":" + item.getValue())); 
    } 
 
    /** 
     * 遍历Map第三种 
     * 通过Map.entrySet遍历key和value，在大容量时推荐使用 
     */ 
    @Test 
    public void testErgodicWayThree() { 
        System.out.println("---------------------Before JAVA8 ------------------------------"); 
        for (Map.Entry<String, Object> entry : map.entrySet()) { 
            System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue()); 
        } 
        System.out.println("---------------------JAVA8 ------------------------------"); 
        map.entrySet().forEach(entry -> System.out.println("key:value = " + entry.getKey() + ":" + entry.getValue())); 
    } 
 
    /** 
     * 遍历Map第四种 
     * 通过Map.values()遍历所有的value，但不能遍历key 
     */ 
    @Test 
    public void testErgodicWayFour() { 
        System.out.println("---------------------Before JAVA8 ------------------------------"); 
        for (Object value : map.values()) { 
            System.out.println("map.value = " + value); 
        } 
        System.out.println("---------------------JAVA8 ------------------------------"); 
        map.values().forEach(System.out::println); // 等价于map.values().forEach(value -> System.out.println(value)); 
    } 
 
    /** 
     * 遍历Map第五种 
     * 通过k,v遍历，Java8独有的 
     */ 
    @Test 
    public void testErgodicWayFive() { 
        System.out.println("---------------------Only JAVA8 ------------------------------"); 
        map.forEach((k, v) -> System.out.println("key:value = " + k + ":" + v)); 
    } 
}