Cannot Implement or extend - java

Question

I have a class C with lots of members(say 10 members) + members that are only in C

I have two more classes A and B which has exactly those above mentioned 10 members. (A and B each does not have those 10 members. Those 10 members are distributed among A and B and A and B has few other fields)

class C {
    private int member1;
    private String member2;
    private String member3;
    private float member4;
    ...
    private String member10;

    private member11_only_in_C;
    private member12_only_in_C;
    ...
}



class A {
    private String memeber10;
    private float member4;
    private double member6;
    ....
}
class B {
     private int memeber1;
     private String memeber2;
     private String member7;
     ....
 }

So when I have cObject I need to set the values of all members in A and B like

aObject.setMember10(cObject.getMember10());
bObject.setMember1(cObject.getMember1());
... and so on for all 10 members

This looks bad(long and in future If i add more members to C,A,B I need to write setters for them). So what I thought was If I have class C extend or implement A and B I can cast it like

 A aObject = (A)cObject;
 B bObject = (B)cObject;

But the problems are

1. Java does not allow multiple inheritance
2. I cannot make A and B as interfaces because I need to set their values. (If I make them as interfaces, their members would become final, which means that I cannot change their values)
3. I cannot extend one class and implement other. (I then cannot set values of members of the interface)

What can I do now?

Thanks..

Answer 1

As I understand it you have two classes A and B, both with a number of fields, and you want to create a third class C with all the fields of A and B.

As you point out you can't do this with inheritance in Java because multiple inheritance of state is not supported.

You can do something similar using composition instead.

public final class C {

    private final A a;
    private final B b;

    public C(A a, B b) {
        this.a = a;
        this.b = b;
    }

    ...

    void setMember7(String s) {
        b.setMember7(s);
    }

    String getMember7() {
        return b.getMember7();
    }

    ...
}

I'm not sure if this is a good idea or what you need though. We would need more information about your use-case.

EDIT

If A and B have fields that are not in C you could make a class A2 with all the fields common to A and C and a class B2 with all the fields common to B and C, like this:

public final class A {

    private final A2 a2;
    // other fields

    public A(A2 a2) { 
        this.a2 = a2;
    }
}

public final class B {

    private final B2 b2;
    // other fields

    public B(B2 b2) {
        this.b2 = b2;
    }
}

public final class C {

    private final A2 a2 = new A2();
    private final B2 b2 = new B2();

    ...

    public void setMember7(String s) {
        b2.setMember7(s);
    }

    public String getMember7() {
        return b2.getMember7();
    }

    ...

    public A getA() {
        return new A(a2);
    }

    public B getB() {
        return new B(b2);
    } 
}

Answer 2

I don't know exactly what you want but i think what you need can be accomplished in the constructor

Class A{
 private member1;
 private member10;
 Class A(){
 }
 Class A(C cObject){
  member1 = cObject.getMember1();
  //the rest of member varaibles you want to set
  member10 = cObject.getMember10();
  }
}
Class B{
 private member1;
 private member10;
 Class B(){
 }
 Class B(C cObject){
  member1 = cObject.getMember1();
  //the rest of member varaibles you want to set
  member10 = cObject.getMember10();
  }
}

to use it :-

 B objectB = new B(objectC);
 A objectB = new A(objectC);