Map集合中定義的方法
阿新 • • 發佈:2021-06-24
新增、刪除、修改操作
Object put(Object key,Object value):將指定key-value新增到(或修改)當前map物件中
void putAll(Map m):將m中的所有key-value對存放到當前map中
Object remove(Object key):移除指定key的key-value對,並返回value
void clear():清空當前map中的所有資料
@Test public void test3(){ Map map = new HashMap(); map.put("AA",123);//新增 map.put(45,123); map.put("BB",56); map.put("AA",87);//修改 System.out.println(map); Map map1 = new HashMap(); map1.put("CC",123); map1.put("DD",123); map.putAll(map1); System.out.println(map); //remove(Object key) Object value = map.remove("CC"); System.out.println(value); System.out.println(map); //clear() map.clear();//與map = null操作不同 System.out.println(map.size()); System.out.println(map); }
元素查詢操作
Object get(Object key):獲取指定key對應的value
boolean containsKey(Object key):是否包含指定的key
boolean containsValue(Object value):是否包含指定的value
int size():返回map中key-value對的個數
boolean isEmpty():判斷當前map是否為空
boolean equals(Object obj):判斷當前map和引數物件obj是否相等
@Test public void test4(){ Map map = new HashMap(); map.put("AA",123); map.put(45,123); map.put("BB",56); //Object get(Object key) System.out.println(map.get(45)); //boolean containsKey(Object key) boolean isExist = map.containsKey("BB"); System.out.println(isExist); isExist = map.containsValue(123); System.out.println(isExist); map.clear(); System.out.println(map.isEmpty()); }
元檢視操作的方法:
Set keySet():返回所有key構成的Set集合
Collection values():返回所有value構成的Collection集合
Set entrySet():返回所有key-value對構成的Set集合
@Test public void test5(){ Map map = new HashMap(); map.put("AA",123); map.put(45,123); map.put("BB",56); //遍歷所有的key集:keySet() Set set = map.keySet(); Iterator iterator = set.iterator(); while (iterator.hasNext()) { System.out.println(iterator.next()); } System.out.println("======================="); //遍歷所有的value集:values() Collection values = map.values(); for(Object obj : values){ System.out.println(obj); } System.out.println("======================="); //遍歷所有的key-value //方式一:entrySet(): Set entrySet = map.entrySet(); Iterator iterator1 = entrySet.iterator(); while (iterator1.hasNext()){ Object o = iterator1.next(); //entrySet集合中的元素都是entry Map.Entry entry = (Map.Entry) o; System.out.println(entry.getKey() + "----->" + entry.getValue()); } System.out.println("======================="); //方式二: Set keySet = map.keySet(); Iterator iterator2 = keySet.iterator(); while (iterator2.hasNext()) { Object key = iterator2.next(); Object value = map.get(key); System.out.println(key + "====" + value); } }
總結
- 增:put(Object key,Object value)
- 刪:remove(Object key)
- 改:put(Object key,Object value)
- 查:get(Object key)
- 長度:size()
- 遍歷:keySet() / values() / entrySet()