这段代码:
public class PMTest
{
private static class Runner { }
private static class Server extends Runner { }
private static class Task
{
public void delegate(Runner runner)
{
System.out.println("Task: " + runner.getClass().getName() +
" / " + this.getClass().getName());
}
}
private static class Action extends Task
{
public void delegate(Server server)
{
System.out.println("Action: " + server.getClass().getName() +
" / " + this.getClass().getName());
}
}
private static void foo(Task task, Runner runner)
{
task.delegate(runner);
}
private static void bar(Action task, Runner runner)
{
task.delegate(runner);
}
private static void baz(Action task, Server runner)
{
task.delegate(runner);
}
public static void main (String[] args)
{
try {
Server server = new Server();
Action action = new Action();
action.delegate(server);
foo(action, server);
bar(action, server);
baz(action, server);
}
catch (Throwable t) {
t.printStackTrace();
}
}
}
产生这个输出:
$ java PMTest
Action: PMTest$Server / PMTest$Action
Task: PMTest$Server / PMTest$Action
Task: PMTest$Server / PMTest$Action
Action: PMTest$Server / PMTest$Action
我可以很清楚地看到,Task 的方法被选择了 Action 的方法。不过,我不明白为什么,因为对象总是知道它们是什么,而且我认为 Java 的后期绑定方法选择能够区分方法签名的差异。调用 tobar()
尤其令人困惑,因为此时task
声明为 an Action
。
如果它有所作为,那就是 Java 6:
$ java -version
java version "1.6.0_14"
Java(TM) SE Runtime Environment (build 1.6.0_14-b08)
BEA JRockit(R) (build R27.6.5-32_o-121899-1.6.0_14-20091001-2113-linux-ia32, compiled mode)
我可以更改我的代码以使其工作,但我想了解它为什么不起作用。谢谢您的帮助!