java如何遍历map的所有的元素（各种方法）

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>();

//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

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));
}
}