Java如何遍历Map的所有的元素

来源：互联网发布：矢量数据是什么意思编辑：程序博客网时间：2024/05/01 06:47

JDK1.4中

Map map = new HashMap();    Iterator it = map.entrySet().iterator();    while (it.hasNext()) {        Map.Entry entry = (Map.Entry) it.next();        Object key = entry.getKey();        Object value = entry.getValue();}

JDK1.5中,应用新特性For-Each循环

Map m = new HashMap();for(Object o : map.keySet()){    map.get(o);}

返回的 set 中的每个元素都是一个 Map.Entry 类型。

private Hashtable<String, String> emails = new Hashtable<String, String>();

另外我们可以先把hashMap 转为集合Collection，再迭代输出，不过得到的对象

 //方法一: 用entrySet()   Iterator it = emails.entrySet().iterator();   while(it.hasNext()){    Map.Entry m=(Map.Entry)it.next();    logger.info("email-" + m.getKey() + ":" + m.getValue());   }     // 方法二：jdk1.5支持，用entrySet()和For-Each循环()   for (Map.Entry<String, String> m : emails.entrySet()) {       logger.info("email-" + m.getKey() + ":" + m.getValue());   }     // 方法三：用keySet()   Iterator it = emails.keySet().iterator();   while (it.hasNext()){    String key;    key=(String)it.next();    logger.info("email-" + key + ":" + emails.get(key));   }// 方法五：jdk1.5支持，用keySEt()和For-Each循环for(Object m: emails.keySet()){    logger.info("email-" + m+ ":" + emails.get(m));   }

Map aa = new HashMap(); aa.put("tmp1", new Object()); //追加替换用同样的函数. aa.remove("temp1"); //删除 for (Iterator i = aa.values().iterator(); i.hasNext(); ) { Object temp = i.next(); } //遍历

来个完整的，包含TreeSet的元素内部排序的

public static void main(String[] args) {   ArrayList<String> list = new ArrayList<String>();   HashMap<Object,Object> hash = new HashMap<Object,Object>();   TreeMap<Object,Object> treeMap = new TreeMap<Object,Object>();   list.add("a");   list.add("b");   list.add("c");     hash.put(3, 3);   hash.put(4, 4);   hash.put(5, 5);   hash.put(6, 6);   hash.put(1, 1);   hash.put(2, 2);     treeMap.put(1, 1);   treeMap.put(2, 2);   treeMap.put(3, 3);   treeMap.put(4, 4);   treeMap.put(5, 5);   treeMap.put(6, 6);     //list遍历   for(String m: list){    System.out.println(m);   }   // hashmap entrySet() 遍历   for(Map.Entry<Object,Object> m: hash.entrySet()){    System.out.println(m.getKey()+"---"+m.getValue());   }   //hashmap keySet() 遍历   for(Object m: hash.keySet()){    System.out.println(m+"---"+hash.get(m));   }   // treemap keySet()遍历   for(Object m: treeMap.keySet()){    System.out.println(m+"---"+treeMap.get(m));   }}