java - 为什么存在WeakHashMap，却没有WeakSet？

Question

来自 J. Bloch

A ... source of memory leaks is listeners ... The best way to ensure that callbacks are garbage collected promptly is to store only weak references to them, for instance, by storing them only as keys in a WeakHashMap.

那么，为什么 Java 中没有 WeakSet Collections framework ?

Answer 1

Collections.newSetFromMap

Set<Object> weakHashSet = 
    Collections.newSetFromMap(
        new WeakHashMap<Object, Boolean>()
    );

如 Collections.newSetFromMap 中所示文档，通过 WeakHashMap获取 Set .