### Question:
Trie implements Serializable { public boolean hasPrefix( String key ) { return ( this.get( key ) != null ); } Trie();   Trie( char key ); void put( String key, V value ); V get( String key ); boolean hasPrefix( String key ); String getCommonPrefix(); @Override String toString();  }### Answer:
@Test public void testHasPrefix() { Trie<String> trie = new Trie<>(); trie.put( "a", "a" ); trie.put( "aa", "aa" ); trie.put( "aaa", "aaa" ); trie.put( "ab", "ab" ); trie.put( "abb", "abb" ); trie.put( "aabb", "aabb" ); assertTrue( trie.hasPrefix( "a" ) ); assertTrue( trie.hasPrefix( "aa" ) ); assertTrue( trie.hasPrefix( "aaa" ) ); assertFalse( trie.hasPrefix( "" ) ); assertFalse( trie.hasPrefix( "5" ) ); assertFalse( trie.hasPrefix( "zzzz" ) ); }