reference - 对 java.util.WeakHashMap 行为感到困惑？

Question

这里是三种情况，为什么 case1 结果是 {name=Bob}，但是 case2 结果是 {}，case3 仍然是 {name=Bob}。case1 和 case2 之间的区别在于放置不同的键。在 JDK8 上运行。为什么？

    //Case1:
    WeakHashMap<String,String> mapCase1 = new WeakHashMap<>();
    mapCase1.put("name", "Bob");
    System.gc();
    Thread.sleep(3000);
    System.out.println(mapCase1); //{name=Bob}
    //Case2:
    WeakHashMap<String,String> mapCase2 = new WeakHashMap<>();
    mapCase2.put(new String("name"), "Bob");
    System.gc();
    Thread.sleep(3000);
    System.out.println(mapCase2); //{}
    //Case3:
    WeakHashMap<String,String> mapCase3 = new WeakHashMap<>();
    String map3Key = new String("name");
    mapCase3.put(map3Key, "Bob");
    System.gc();
    Thread.sleep(3000);
    System.out.println(mapCase3); //{name=Bob}