Java 简明教程
Java WeakHashMap Class
Introduction
Java WeakHashMap 类是基于散列表的 Map 实现，其具有弱键。如果不再使用其键，则垃圾回收器将自动删除 WeakHashMap 中的条目。以下是有关 WeakHashMap 的重点 −
The Java WeakHashMap class is a hashtable-based Map implementation with weak keys. An entry in a WeakHashMap will automatically be removed by the garbage collector, when its key is no longer in use. Following are the important points about WeakHashMap −
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Both null values and the null key are supported.
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Like most collection classes, this class is also not synchronized.
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This class is intended primarily for use with key objects whose equals methods test for object identity using the == operator.
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Each key object in a WeakHashMap is stored indirectly as the referent of a weak reference.
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This class is a member of the Java Collections Framework.
Class declaration
以下是 java.util.WeakHashMap 类的声明 -
Following is the declaration for java.util.WeakHashMap class −
public class WeakHashMap<K,V>
extends AbstractMap<K,V>
implements Map<K,V>此处 <K> 是此映射维护的键的类型，而 <V> 是映射值的类型。
Here <K> is the type of keys maintained by this map and <V> is the type of mapped values.
Methods inherited
此类从以下类中继承方法：
This class inherits methods from the following classes −
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java.util.AbstractMap
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java.lang.Object
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java.util.Map
Adding a Key-Value Pair to a WeakHashMap of Integer, Integer Pairs Example
以下示例展示了在映射中放置少数值的 Java WeakHashMap put() 方法的用法。我们创建了一个整数、整数对的映射对象。接着使用 put() 方法添加了几条记录，然后打印映射。
The following example shows the usage of Java WeakHashMap put() method to put few values in a Map. We’ve created a Map object of Integer,Integer pairs. Then few entries are added using put() method and then map is printed.
package com.tutorialspoint;
import java.util.WeakHashMap;
public class WeakHashMapDemo {
public static void main(String args[]) {
// create hash map
WeakHashMap<Integer,Integer> newmap = new WeakHashMap<>();
// populate hash map
newmap.put(1, 1);
newmap.put(2, 2);
newmap.put(3, 3);
System.out.println("Map elements: " + newmap);
}
}