Java如何遍历Map的所有的元素

JDK1.4中

Java代码

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();   
} 

  

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);
}

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>();

    //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));
   }

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

   //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));
   }

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

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

   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));
   }
}