Map接口的常用方法

一、添加、删除、修改

put(Object key, Object value)

Map map = new HashMap();

System.out.println("---put(Object key, Object value)---添加和修改");
//添加
map.put("AA", 123);
map.put(45, 123);
map.put("BB", 56);
System.out.println(map);        //{AA=123, BB=56, 45=123}
//修改
map.put("AA", 87);
System.out.println(map);    //{AA=87, BB=56, 45=123}

putAll(Map m)

System.out.println("---putAll(Map m)---");
//putAll()
Map map1 = new HashMap();
map1.put("CC", 123);
map1.put("DD", 123);

map.putAll(map1);

System.out.println(map);    //{AA=87, BB=56, CC=123, DD=123, 45=123}

remove(Object key)

System.out.println("---remove(Object key)---");
//remove(Object key)        返回移除的key所对应的value值
Object value = map.remove("CC");
System.out.println(value);      //123
System.out.println(map);        //{AA=87, BB=56, DD=123, 45=123}

clear()

System.out.println("---clear()---");
map.clear();
System.out.println(map);        //{}
System.out.println(map.size()); //0

二、元素查询

get(Object key)

Map map = new HashMap();

map.put("AA", 123);
map.put(45, 123);
map.put("BB", 56);

System.out.println("---get(Object key)---获取指定key的value");
Object value = map.get("BB");
System.out.println(value);		//56

containsKey(Object key)

//containsKey()
System.out.println("---containsKey(Object key)---是否包含指定的key");
boolean isExist = map.containsKey("BB");
System.out.println(isExist);        //true

containsValue(Object value)

//containsValue()
System.out.println("---containsValue(Object value)---是否包含指定的value");
isExist = map.containsValue(123);
System.out.println(isExist);        //true

size()

//size()
System.out.println("---size()---返回map中key-value对的个数");
int size = map.size();
System.out.println(size);       //3

isEmpty()

//isEmpty()
System.out.println("---isEmpty---判断当前map是否为空");
boolean isEmpty = map.isEmpty();
System.out.println(isEmpty);        //false

equals(Object obj)

//equals(Obejct obj)
System.out.println("---equals()---判断当前map和参数对象obj是否相等");
Map map1 = new HashMap();
map1.put("AA", 123);
map1.put(45, 123);
map1.put("BB", 56);
boolean isequals = map.equals(map1);
System.out.println(isequals);       //true

三、元视图操作的方法

keySet()

Map map = new HashMap();

map.put("AA", 123);
map.put(45, 123);
map.put("BB", 56);

//keySet()
System.out.println("---keySet()---返回所有key构成的Set集合");
Set set = map.keySet();
Iterator iterator = set.iterator();
while (iterator.hasNext()){
    System.out.println(iterator.next());
}

values()

//values()
System.out.println("---values()---返回所有value构成的Collection集合");
Collection values = map.values();
Iterator iterator1 = values.iterator();
while (iterator1.hasNext()){
    System.out.println(iterator1.next());
}

entrySet()

//entrySet()
System.out.println("---entrySet()---返回所有key-value对构成的Set集合");
Set entrySet = map.entrySet();
Iterator iterator2 = entrySet.iterator();
while (iterator2.hasNext()){
    System.out.println(iterator2.next());
}

总结：

添加：put()/putAll()

删除：remove()

修改：put()

查询：get()

长度：size()

遍历：keySet()/values()/entrySet()