Triple Inheritance

[Samaras]

I remember that i had read that multi inheritance is not allowed in JAVA.So imagine the hierarchy is like this in my code

A
|
|
v
B
|
|
v
C

An ugly way to make C inherit what comes from A is to write the vary same functions to function B and to call the functions of A there.Isn't there a more elegant-smart way to do this?

The variables can not be inheritted in any way?

[Samaras]

I also thought that we were able to use the same functionality with the interfaces(a class can implement two or more intrefaces if wanted) but i do not think that is works for the class inheritance.

[copeg]

I don't understand the inheritance structure you wrote, but if you want 'multiple' inheritance - which you cannot directly do in java - use interfaces. Imagine the following: A is an interface, implemented by Aimpl. B is an interface, implemented by the class Bimpl. You wish C to inherit from A and B (actually inherit from Aimpl and Bimpl), then C implements A and B. C can then delegate the the appropriate method calls to instances of Aimpl and Bimpl, and override/extend the behavior it wishes to.

For instance, a very simple and poor example - forgive the poor naming, lack of commentary, and lack of this actually doing anything interesting:

public interface A{
    public void doA();
}
public class Aimpl implements A{
    @Override
    public void doA(){
        System.out.println("A");
    }
}
 
public interface B{
    public void doB();
}
public class Bimpl implements B{
    @Override
    public void doB(){
        System.out.println("B");
    }
}
 
public class C implements A, B{
    private A ai = new Aimpl();
    private B bi = new Bimpl();
 
    @Override
    public void doA(){
        ai.doA();
    }
    @Override
    public void doB(){
        bi.doB();
    }
}

[pbrockway2]

Your original post suggests you want B to extend A, and C to extend B. And that's fine - ie the following compiles:

class A {}
class B extends A {}
class C extends B {}

Java doesn't allow classes to inherit the implementation of multiple direct or immediate super classes, but that's all. Animal species, genera etc are the same: but a cat can be-a feline and a mammal.

[Samaras]

Copeg i also thought of what you said but i think is too much.

pbrocway2 check this example.

Inheritance.java

package inheritance;
 
public class Inheritance {
    public static void main(String[] args) {
        C test=new C();
        test.foo();
        test.bla();
    }
}

A.java

package inheritance;
 
public class A {
    private int year;
    public  int getYear(){
        return year;
    }
}

B.java

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package inheritance;
 
/**
 *
 * @author User
 */
public class B extends A {
    private int day;
 
    public final int getDay(){
        return day;
    }
 
    public void foo(){
        int year=super.getYear();
        day=15;
    }
 
}

C.java

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package inheritance;
 
/**
 *
 * @author User
 */
public class C extends B {
    public void bla(){
        int day=super.getDay();
        int year=super.getYear();
    }
}

this works good but in a larger program i have now i can not achieve this.Something else might be the problem.I am going to look it up
thanks

[pbrockway2]

You don't need those "super" keywords.

Instances of C are also instances of B and they are also instances of A. So it is perfectly acceptable (and clearer) to write

package inheritance;
 
public class C extends B {
    public void bla(){
        int day = getDay();
        int year = getYear();
    }
}

[psabbate]

You can inherit attributes but should be careful regarding their access modifier. Only protected attributes can be accessed directly by sub classes.

[copeg]

Only protected attributes can be accessed directly by sub classes.

Perhaps you mean only protected and public Controlling Access to Members of a Class (The Java™ Tutorials > Learning the Java Language > Classes and Objects)

[lightOfDay]

There are some options, ranging from elegant to down right ugly, depending on the need for this "double inheritance" (I believe it's not triple). Without a hard example, I don't think I can really figure out the best way to achieve the desired effect.