Java中遍历Map的六种方法实现

/**
 * 1.获取全部的key值
 */
public void testMap1(){
    HashMap<String, Object> map = new HashMap<>();
    Set<String> keySet = map.keySet();
    for (String key: keySet){
        System.out.println(key);
    }
}

/**
 * 2.获取全部的value值
 */
public void testMap2(){
    HashMap<String, Object> map = new HashMap<>();
    Collection<Object> values = map.values();
    for (Object value: values){
        System.out.println(value);
    }
}

/**
 * 3.通过遍历key值获取value值
 */
public void testMap3(){
    HashMap<String, Object> map = new HashMap<>();
    Set<String> keySet = map.keySet();
    for (String key: keySet){
        Object value = map.get(key);
        System.out.println(value);
    }
}

/**
 * 4.通过entrySet()方法，进行遍历
 */
public void testMap4(){
    HashMap<String, Object> map = new HashMap<>();
    Set<Map.Entry<String, Object>> entrySet = map.entrySet();
    for (Map.Entry<String, Object> entry: entrySet){
        // entry代表map元素的一个对象，通过对象调用getValue()方法，获取value数据，也可以调用getKey()方法，获取key值
        Object value = entry.getValue();
        System.out.println(value);
    }
}

/**
 * 5.使用lambda表达式
 */
public void testMap5(){
    HashMap<String, Object> map = new HashMap<>();
    map.forEach((key,value)->{
        // 直接获取key值和value值
        System.out.println("key: " + key + "value: " + value);
    });
}

/**
 * 6.采用迭代器方式，方便进行元素的删除操作
 */
@Test
public void testMap6(){
    HashMap<String, Object> map = new HashMap<>();
    map.put("77","6666");
    Iterator<Map.Entry<String, Object>> iterator = map.entrySet().iterator();
    while (iterator.hasNext()){
        Map.Entry<String, Object> entry = iterator.next();
        if (entry.getKey().equals("77")){
            iterator.remove();
        }
    }
}