public Set<K> keySet() {
        Set<K> ks = keySet;             [color=#0000FF]//这个keySet是什么？ 没有定义啊？[/color]
        return (ks != null ? ks : (keySet = new KeySet()));
    }

public Set<K> keySet() {
    if (keySet == null) {
        keySet = new AbstractSet<K>() {
        public Iterator<K> iterator() {
            return new Iterator<K>() {
            private Iterator<Entry<K,V>> i = entrySet().iterator();

            public boolean hasNext() {
                return i.hasNext();
            }

            public K next() {
                return i.next().getKey();
            }

            public void remove() {
                i.remove();
            }
                    };
        }

        public int size() {
            return AbstractMap.this.size();
        }

        public boolean contains(Object k) {
            return AbstractMap.this.containsKey(k);
        }
        };
    }
    return keySet;
    }

------解决方案--------------------

一定是存在的变量了啦，好好找找。