How to create a classC that act as either classA or classB

Question

How to create a common class that can act as either of two class depending on need.

I tried using

1. Object
2. ArrayList list
3. class classC extends classA, classB

But I didn't get result as expected,

public class classA{
    int value = 1;
}
public class classB{
    int value = 2;
}
public class classC{
    Object commonClass;
    classC(classA a){
        commonClass = a;
    }
    classB(classB b){
        commonClass = b;
    }
    int getValue(){
        return commonClass.value;
    }
}
public static void main(String args[])
{  
    classC c1 = new classC(new classA);
    classC c2 = new classC(new classB);
    
    System.out.println(c1.getValue());  
    System.out.println(c2.getValue());  
}  
/*
 output must be
 c1.getValue() => 1
 c2.getValue() => 2
*/

Answer 1

@LouisWasserman 's point is a good one. You'd probably be better off creating a common superclass. But in terms of your existing code:

public class classC{
    Object commonClass;
    classC(classA a){
        commonClass = a;
    }
    //This constructor is wrong. It needs to be classC(classB b)
    classB(classB b){
        commonClass = b;
    }
    int getValue(){
       //You need a cast here
       // return commonClass.value;
       if (commonClass instanceof classA) {
         return ((classA) commonClass).value;
       } else {
         return ((classB) commonClass).value;
       }
    }
}
public static void main(String args[])
{
  //you need parentheses for creating your objects  
//    classC c1 = new classC(new classA);
//    classC c2 = new classC(new classB);
    classC c1 = new classC(new classA());
    classC c2 = new classC(new classB());
}