How to decide whether use IS A or HAS A Relation

[Ravi Kiran Va]

public class B {

    public String getMe()
    {
        return "Some";
    }
}

Assume that i have a above class , by which parameters should we decide what to use ?? Whether is a or Has a Relation ??

HAS - A

public class A {



    public static void main(String args[])
    {
        B b = new B();
        System.out.println(b.getMe());
    }
}

or

public class A  extends B
{


    public static void main(String args[])
    {
        A b = new A();
        System.out.println(b.getMe());
    }
}

[Jesper de Jong]

It depends on what you are modelling. Most of the time, if you're thinking about a concrete problem domain, it will be clear to you whether there is an "is a" or a "has a" relation between the things that you are modelling.

For example, suppose that you want to model a car. Clearly, a car has an engine, wheels, etc. And a car is a transportation device, etc.