Question

今天，我打开了jre1.6.0_27 HashMap values（）方法源代码

  389  public Set<K> keySet()
  390  {
  391      Set localSet = this.keySet;
  392      return (this.keySet = new KeySet(null));
  393  }
  394
  395  public Collection<V> values()
  396  {
  397      Collection localCollection = this.values;
  398      return (this.values = new Values(null));
  399  }

我认为这些源代码是错误的，但我不知道为什么它们看起来像这样。谁能告诉我为什么？

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谢谢大家，我认为这是Eclipse问题，这个源代码我使用了Eclipse F3并且去了它，所以看起来就像上面那样。

我只是打开src.zip，这个方法源代码是对的。

/**
 * Returns a {@link Collection} view of the values contained in this map.
 * The collection is backed by the map, so changes to the map are
 * reflected in the collection, and vice-versa.  If the map is
 * modified while an iteration over the collection is in progress
 * (except through the iterator's own <tt>remove</tt> operation),
 * the results of the iteration are undefined.  The collection
 * supports element removal, which removes the corresponding
 * mapping from the map, via the <tt>Iterator.remove</tt>,
 * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
 * <tt>retainAll</tt> and <tt>clear</tt> operations.  It does not
 * support the <tt>add</tt> or <tt>addAll</tt> operations.
 */
903    public Collection<V> values() {
904        Collection<V> vs = values;
905        return (vs != null ? vs : (values = new Values()));
906    }

Answer 1

至少在OpenJDK 7中看起来是正确的：

  880       public Set<K> keySet() {
  881           Set<K> ks = keySet;
  882           return (ks != null ? ks : (keySet = new KeySet()));
  883       }

  916       public Collection<V> values() {
  917           Collection<V> vs = values;
  918           return (vs != null ? vs : (values = new Values()));
  919       }

Answer 2

为什么你认为这些方法有误？您必须查看KeySet内的内部类Values和HashMap的源代码，以了解这些内容如何工作。

keySet()方法返回一个新的KeySet对象。在JDK 1.6.0_35中，内部类KeySet的源代码如下所示：

private final class KeySet extends AbstractSet<K> {
    public Iterator<K> iterator() {
        return newKeyIterator();
    }
    public int size() {
        return size;
    }
    public boolean contains(Object o) {
        return containsKey(o);
    }
    public boolean remove(Object o) {
        return HashMap.this.removeEntryForKey(o) != null;
    }
    public void clear() {
        HashMap.this.clear();
    }
}

这是Set的实施，可以从HashMap获取数据。

同样地，内部类Values以相同的方式工作。

jre1.6.0_27 HashMap values（）源代码

2 个答案: