map集合遍历方式

【常用方法】

    HashMap hm=new HashMap();
    //通过制定键替换键所指向的值
    hm.replace(2, "wxz");
    System.out.println(hm.get(2));

    //清空
    hm.clear();
    System.out.println(hm.size());

    //判断是否为空
    System.out.println(hm.isEmpty());

    //是否包含某个键
    System.out.println(hm.containsKey(9));

    //是否包含某个值
    System.out.println(hm.containsValue("wxz"));

    //可以用null作为键，也可以用null做为值
    hm.put(null, null);

【遍历方式】

1. 遍历所有的键,并通过键获取值

    Set keySet = map.keySet();
    Iterator ite = keySet.iterator();
    while(ite.hasNext()){
        Object key = ite.next();
        Object value = map.get(key);
        System.out.println("key:" + key + "   value:" + value);
    }   

2. 获取所有的值，实际用处不大

    Collection coll = map.values();
    for(Object obj: coll){
        System.out.println(obj);
    }       

3. 获取键值对的映射关系

    Set entrySet = map.entrySet();
    Iterator ite1 = entrySet.iterator();
    while(ite1.hasNext()){
        Object obj = ite1.next();
        //Entry包含一对映射
        Entry entry = (Entry)obj;
        System.out.println("key:" + entry.getKey() + "  value: " +                  entry.getValue());
    }

4. Map.Entry< String, String>方式一

for(Map.Entry<String, String> entry:map.entrySet()){    
    System.out.println(entry.getKey()+"--->"+entry.getValue());  
}  

5.Map.Entry< String, String>方式二

Set set = map.entrySet();         
Iterator i = set.iterator();         
while(i.hasNext()){      
     Map.Entry<String, String> entry1=(Map.Entry<String, String>)i.next();    
     System.out.println(entry1.getKey()+"=="+entry1.getValue());    
}