Java种遍历Map集合的几种常用方式

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public class TestMap {public static void main(String[] args) {Map<String, String> map = new HashMap<String, String>();map.put("key1", "value1");map.put("key2", "value2");map.put("key3", "value3");//method1(map);//method2(map);//method3(map);method4(map);}//第一种：普遍使用，二次取值public static void method1(Map<String, String> map) {System.err.println("通过Map.keySet遍历");Iterator<String> it = map.keySet().iterator();while (it.hasNext()) {String key = it.next();String value = map.get(key);System.err.println("key=" + key + " and value=" + value);}System.err.println("====================================");for (String key : map.keySet()) {System.err.println("key=" + key + " and value=" + map.get(key));}}//第二种：通过Map.entrySet使用iterator遍历key和valuepublic static void method2 (Map<String, String> map) {Iterator it = map.entrySet().iterator();while (it.hasNext()) {Map.Entry entry = (Entry) it.next();String key = (String) entry.getKey();String value = (String) entry.getValue();System.err.println("key=" + key + " and value=" + value);}}//第三种：推荐，尤其是容量较大的，通过Map.entrySet遍历key和valuepublic static void method3(Map<String, String> map){for (Entry<String, String> entry : map.entrySet()) {System.err.println("key=" + entry.getKey() + " and value=" + entry.getValue());}}//第四种：通过Map.values()遍历所有的value，但不能遍历keypublic static void method4 (Map<String, String> map) {for (String value : map.values()) {System.err.println("value=" + value);}}}
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