Java如何遍历Map的所有的元素

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));

}

}