Java8遍历Map - smile0821/learngit GitHub Wiki

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));
}

}