Re: Query regarding java Multiple Inheritance

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 26 Nov 2009 23:31:05 -0500

Message-ID:

<4b0f55fe$0$278$14726298@news.sunsite.dk>

Amit Jain wrote:

Hi All,
I am new to Java and need your views for my query.

What will be the solution for implementint two Interface in a single
class A if these interfaces I1 and I2 are written as mentioned below:
interface I1{
void method ();
long square(long i);
}

interface I2{
String method();
long squareRoot(long i);
}

class A implements I1, I2{
void method(){
System.out.println("--- Hi ----");
}
// implementation of square() and squareRoot() method
}

Above implementation of interface in class A will never complies
because of "void method();" declared in both I1 and I2. And we want
the implementation of I1 and I2 in class A only. How can we acheive
this in such situations.

Java does not allow this construct. You need a workaround.

I once created the example below to illustrate a
possible workaround which I believe is a reasonable good
one.

Arne

========================

public class MultiInterf {
     public static void main(String[] args) {
         A o = new A();
         System.out.println(o.asB().f());
         System.out.println(o.asC().f());
     }
}

interface B {
     Object f();
}

interface C {
     boolean f();
}

class A {
     public Object fB() {
         return null;
     }
     public boolean fC() {
         return false;
     }
     public B asB() {
         return new AB(this);
     }
     public C asC() {
         return new AC(this);
     }
     private static class AB implements B {
         private A real;
         public AB(A real) {
             this.real = real;
         }
         public Object f() {
             return real.fB();
         }
     }
     private static class AC implements C {
         private A real;
         public AC(A real) {
             this.real = real;
         }
         public boolean f() {
             return real.fC();
         }
     }
}