JAVA8獨(dú)有的map遍歷方式(非常好用)

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');
  }


  /**
   * 遍歷Map的方式一
   * 通過Map.keySet遍歷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)));
  }

  /**
   * 遍歷Map第二種
   * 通過Map.entrySet使用Iterator遍歷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()));
  }

  /**
   * 遍歷Map第三種
   * 通過Map.entrySet遍歷key和value，在大容量時推薦使用
   */
  @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()));
  }

  /**
   * 遍歷Map第四種
   * 通過Map.values()遍歷所有的value，但不能遍歷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); // 等價于map.values().forEach(value -> System.out.println(value));
  }

  /**
   * 遍歷Map第五種
   * 通過k,v遍歷，Java8獨(dú)有的
   */
  @Test
  public void testErgodicWayFive() {
    System.out.println("---------------------Only JAVA8 ------------------------------");
    map.forEach((k, v) -> System.out.println("key:value = " + k + ":" + v));
  }
}