public V put(K key, V value) { Entry<K,V> t = root; if (t == null) { compare(key, key); // type (and possibly null) check root = new Entry<>(key, value, null); size = 1; modCount++; return null; } 加上String str1=(String)o1;String str2=(String)o1;所以输出结果怎么只有abcd |