Calling a method of a class using an argument of a method which is an object of that class

Question

Consider the following classes

Class A{
    public void m1(){
          System.out.println("test in A.m1()");
    }

    public void m2(){
          //do something a
    }
}


Class B{
    public void m1(){
          //do something b
    }

    public void m2(){
          //do something b
    }
}


Class C{
    public void m1(){
          //do something c
    }

    public void m2(){
          //do something c
    }
}

Class T{
    public void m3(Object obj1){
          obj1.m1();
    }

    public void m4(Object obj1){
          A a=new A();
          m3(a);
    }


}

So now my question is, is there any way I can send an open object to a method which will detect what type of object it is and call method of that object class. In this example I am hoping to see the output: "test in A.m1()"

This is a task for the Visitor pattern.

user207421
– user207421

2012-12-22 02:01:54 +00:00
Commented Dec 22, 2012 at 2:01 — user207421
– user207421, Commented Dec 22, 2012 at 2:01

Ash · Accepted Answer · 2012-12-22 01:55:14Z

3

You can use Java's Reflection API to query an arbitrary object to see if it has a method named m1 or m2 and then invoke it. But that is pretty ugly.

Is there anything from stopping you using an interface? Example below (where "..." indicates places where you would put your specific implementation):

interface MyMethods {
  public void m1();
  public void m2();
}

class A implements MyMethods {
  public void m1() { ... }
  public void m2() { ... }
}

class B implements MyMethods {
  ...
}

class C implements MyMethods {
  ...
}

class T {
  public void m3(MyMethods obj1) {
    obj1.m1();
  } 

  public void m4(Object obj1) {
    // Call m3 three times with different object instance types...
    A a = new A();
    m3(a);
    B b = new B();
    m3(b);
    C c = new C();
    m3(c);
  }
}

edited Dec 22, 2012 at 1:55

answered Dec 22, 2012 at 1:45

Ash

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2 Comments

LynAs Over a year ago

i know how to use interface in this case. but i was wondering if it can be done the way i explained. thanks for your answer though.

Ash Over a year ago

What I think you're describing is essentially duck typing, and is a feature of dynamically-typed languages. Java doesn't allow that without a bit of effort to work around things.

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