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>(); //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)); } }