java - WeakHashMap示例

我创建一个WeakHashMap作为

WeakHashMap<Employee,String> map = new WeakHashMap<Employee,String>();
map.put(emp,"hello");

其中emp是Employee对象。现在，如果我执行emp = null或说不再引用emp对象，那么将条目从WeakHashMap中删除，即Map的大小是否为零？如果是HashMap，情况会相反吗？
我对WeakHashMap的理解正确吗？

最佳答案

一个非常简单的例子，可以启发已经说过的话:

import java.util.WeakHashMap;

public class WeakHashMapDemo {

    public static void main(String[] args) {
        // -- Fill a weak hash map with one entry
        WeakHashMap<Data, String> map = new WeakHashMap<Data, String>();
        Data someDataObject = new Data("foo");
        map.put(someDataObject, someDataObject.value);
        System.out.println("map contains someDataObject ? " + map.containsKey(someDataObject));

        // -- now make someDataObject elligible for garbage collection...
        someDataObject = null;

        for (int i = 0; i < 10000; i++) {
            if (map.size() != 0) {
                System.out.println("At iteration " + i + " the map still holds the reference on someDataObject");
            } else {
                System.out.println("somDataObject has finally been garbage collected at iteration " + i + ", hence the map is now empty");
                break;
            }
        }
    }

    static class Data {
        String value;
        Data(String value) {
            this.value = value;
        }
    }
}

输出:

    map contains someDataObject ? true
    ...
    At iteration 6216 the map still holds the reference on someDataObject
    At iteration 6217 the map still holds the reference on someDataObject
    At iteration 6218 the map still holds the reference on someDataObject
    somDataObject has finally been garbage collected at iteration 6219, hence the map is now empty

关于java - WeakHashMap示例，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/10599710/