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)); } }