How do I know what class called the abstract method?

Question

say there are 2 classes...

public class NotAbstract1 extends AnAbstract {
  NotAbstract1() { super(); }
}

public class NotAbstract2 extends AnAbstract {
  NotAbstract2() { super(); }
}

public abstract class AnAbstract {
  AnAbstract() { //do something }
  abstract void saySomething() { System.out.println("Something"); }
}

In this example, NotAbstract1 and NotAbstract2 can call saySomething() . How can I, from within the saySomething() method of AnAbstract , recognize the class which called it? Without passing in the class or an identifier .

Again, the easy solution is to change the method signature to be saySomething(Class clazz) but I'd like to not do that. I have a feeling it can be done with reflection so I'm adding that tag to the question.

Answer 1

您可以在saySomething() this.getClass()处调用saySomething() - 它会返回当前实例的类型 - notAbstract1或notAbstract2 。

Answer 2

First of all, this line will not compile:

abstract void saySomething() { System.out.println("Something"); }

You cannot both use abstract modifier and provide a method body.

For printing the caller's class, you can write:

void saySomething() {
    System.out.println(this.getClass().toString());
}

Answer 3

The abstract keyword in

abstract void saySomething();

is a place holder. There cannot be code associated with it. What it does is ensure that

public class NotAbstract1
public class NotAbstract2

both have a real implementations like so

public class NotAbstract1 extends AnAbstract {
   void saySomething() {
     System.out.println("I'm NotAbstract1");
   }
}

public class NotAbstract2 extends AnAbstract {
   void saySomething() {
     System.out.println("I'm NotAbstract2");
   }
}

The compiler does these verifications that the saySomething() method exists in the sub classes when you compile NotAbstract1 and NotAbstract2 .

When you are holding a

AnAbstract object = .... get it from somewhere ...

You will be holding either a NotAbstract1 a NotAbstract2 or some other subclass of AnAbstract , but you will be holding as an AnAbstract type.

When you call

AnAbstract object = .... get it from somewhere ...
object.saySomething();

If the object was originally constructed as a NotAbstract1 you would run

System.out.println("I'm NotAbstract1");

If the object was originally constructed as a NotAbstract2 you would run

System.out.println("I'm NotAbstract2");  

If the object was some other kind of AnAbstract you would run whatever was in that sub-class's definition of saySomething() .

Answer 4

尽管您可以在 saySomething() 中使用 this.getClass() 进行检查，但是如果您想根据从哪个类调用此方法来使该方法具有不同的行为，则理想情况下应该覆盖这些类中的 saySomething() 方法。