題組內容

七、 public class X {public String whatIAm() {return “I’m an X.”;}} public class Y extends X {public String whatIAm() {return “I’m a Y.”;}} public static void main(String[] args) throws IOException { X x; BufferedReader reader = new BufferedReader (new InputStreamReader(System.in)); if (reader.readLine().equals(“Go with X”)) x = new X(); else x = new Y(); System.out.println(x.whatIAm()); } // main

⑵請以此程式解釋動態繫結（dynamic binding）。（10 分）