遍历Map的4种方法

水深无声 2022-09-11 01:23 168阅读 0赞

package junit;
    
    import java.util.HashMap;
    import java.util.Iterator;
    import java.util.Map;
    
    public class TestDemo { 
        public static void main(String[] args) { 
            Map<String, String> map = new HashMap<String, String>();
            map.put("1", "value1");
            map.put("2", "value2");
            map.put("3", "value3");
            methodOne(map);
            //第二种(3分)
    // methodTwo(map);
            //第三种
    // methodThree(map);
            //第四种(2分)
    // methodFour(map);
        }
        private static void methodOne(Map<String, String> map) { 
            //第一种：普遍使用，二次取值(3分)
            System.out.println("通过Map.keySet遍历key和value：");
            for (String key : map.keySet()) { 
                System.out.println("key= "+ key + " and value= " + map.get(key));
            }
        }
        private static void methodTwo(Map<String, String> map) { 
            System.out.println("通过Map.entrySet使用iterator遍历key和value：");
            Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
            while (it.hasNext()) { 
                Map.Entry<String, String> entry = it.next();
                System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
            }
        }
        private static void methodThree(Map<String, String> map) { 
            //第三种：推荐，尤其是容量大时(2分)
            System.out.println("通过Map.entrySet遍历key和value");
            for (Map.Entry<String, String> entry : map.entrySet()) { 
                System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
            }
        }
        private static void methodFour(Map<String, String> map) { 
            System.out.println("通过Map.values()遍历所有的value，但不能遍历key");
            for (String v : map.values()) { 
                System.out.println("value= " + v);
            }
        }
    
    }