📅 最后修改于: 2020-11-14 06:17:00 🧑 作者: Mango
java.util.HashMap类是基于哈希表的Map接口实现。以下是有关HashMap的要点-
此类无法保证地图的迭代顺序；特别是，它不能保证顺序会随着时间的推移保持恒定。
此类允许空值和空键。
以下是java.util.HashMap类的声明-
public class HashMap
extends AbstractMap
implements Map, Cloneable, Serializable
以下是java.util.HashMap类的参数-
K-这是此映射维护的键的类型。
V-这是映射值的类型。
| Sr.No. | Constructor & Description |
|---|---|
| 1 |
HashMap() This constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75). |
| 2 |
HashMap(Collection c) This constructs an empty HashMap with the specified initial capacity and the default load factor (0.75). |
| 3 |
HashMap(int initialCapacity, float loadFactor) This constructs an empty HashMap with the specified initial capacity and load factor. |
| 4 |
HashMap(Map m) This constructs a new HashMap with the same mappings as the specified Map. |
| Sr.No. | Method & Description |
|---|---|
| 1 | void clear()
This method removes all of the mappings from this map. |
| 2 | Object clone()
This method returns a shallow copy of this HashMap instance, the keys and values themselves are not cloned. |
| 3 | boolean containsKey(Object key)
This method returns true if this map contains a mapping for the specified key. |
| 4 | boolean containsValue(Object value)
This method returns true if this map maps one or more keys to the specified value. |
| 5 | Set This method returns a Set view of the mappings contained in this map. |
| 6 | V get(Object key)
This method returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. |
| 7 | boolean isEmpty()
This method returns true if this map contains no key-value mapping. |
| 8 | Set This method returns a Set view of the keys contained in this map. |
| 9 | V put(K key, V value)
This method associates the specified value with the specified key in this map. |
| 10 | void putAll(Map m)
This method copies all of the mappings from the specified map to this map. |
| 11 | V remove(Object key)
This method removes the mapping for the specified key from this map if present. |
| 12 | int size()
This method returns the number of key-value mappings in this map. |
| 13 | Collection This method returns a Collection view of the values contained in this map. |
此类从以下类继承方法-