【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());
}