CODEWITHSUNDEEP
javaclassobjectinheritance
user2303321
user2303321

Reputation: 327

How to use Class Objects with Inheritance

I have a parent class, Parent, with two child classes, A and B. A have a class, Wrapper, that contains an interface, Function, which allows the programmer to specify a particular method for each wrapper.

Wrapper contains the variables, Class<Parent> inputClass and Class<Parent> outputClass, which specify the input and output type. Wrapper is supposed to map an A to an A or B, or a B to an A or B.

My problem arises when I try to call the wrapper constructor, Wrapper(Class<Parent> input, Class<Parent> output, Function func). Eclipse gives me an error for trying to put an A.class or B.class in for either input or output. Given that A and B are child classes of Parent, I thought they would be able to pass into the constructor. How can I implement this?

public class Parent {
    protected int value;
    public void setValue(int x){ value = x; }
    public int getValue(){ return value; }
}


public class A extends Parent{
    public A(){ setValue(1); }
    public A(B b){ setValue( b.getValue()); }
}

public class B extends Parent{
    public B(){ setValue(2); }
    public B(A a){ setValue(a.getValue()); }
}


public class Wrapper{
    protected Class<? extends Parent> inputClass;
    protected Class<? extends Parent> outputClass;
    protected interface Function{
        public Parent of(Parent input);
    }
    protected Function function;
    public Wrapper(Class<? extends Parent> in, Class<? extends Parent> out, Function func) {
        inputClass = in;
        outputClass = out;
        function = func;
    }

    public Parent of(Parent input){
        try{
            Parent output = function.of( inputClass.getConstructor( input.getClass() ).newInstance(input) );
            return outputClass.getConstructor( output.getClass() ).newInstance( output );
        } catch(Exception e){
            e.printStackTrace();
            return null;
        }
    }
}

public class Main {
    public static void main(String[] args){
        ///Error occurs here. Can't take A.class in for Parent.class
        Wrapper wrapper = new Wrapper(A.class,B.class, new Function(){
            @Override
            public Parent of(Parent p) {
                return null;
            }
        });     
    }
}

Upvotes: 0

Views: 48

Answers (1)

user2303321
user2303321

Reputation: 327

The problem wasn't from A.class or B.class, but from the interface Function being nested within the Wrapper class. I needed to write new Wrapper.Functionin the constructor in main.

Upvotes: 1

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