How to design this following structure in Java?

I have an interface named SHAPE. CIRCLE and RECTANGLE are two cla开发者_高级运维sses implementing this interface. Now I have to write a class (i have an option to write a class only) CIRCULARRECTANGLE which will extend the properties of CIRCLE and RECTANGLE. How to do this in Java?

You can't do this directly. A Java class can always only extend a single class.

You could use delegation to get a similar effect. Your CircularRectangle (whatever that may represent!) could reference a Circle and a Rectangle object and "present" their properties as its own.

We can't define a class that is-a Circle and a Rectangle - as long as both entities are classes.

To solve a problem where this kind of schizophrenic behaviour is desired, we can consider using the adapter pattern (assuming, we have a Circle and Rectangle interface and concrete implementations)

public class CircleImpl implements Circle {

  // fields, constructors, implemented Circle methods

 public Object adapt(Class<? extends Shape> adaptee) {

   if (adaptee == Rectangle.class) {
     return new Rectangle() {
        // implemented rectangle methods so that
        // we have a squared circle
     };
   }
   return null;
 }
}

Since Java extends one class at a time, you will need to create abstract classes to fit your criteria.

Example:

public abstract class AbstractRectangle extends Rectangle {

public abstract class AbstractCircularRectangle extends AbstractRectangle {

public class CircularRectangle extends AbstractCircularRectangle {

Update: My first attempt will never work, hence my update:

Since my first attempt never extended a Circle, you will need to keep reference to eiter a Circle or a Rectangle like so:

public class CircularRectangle extends Rectangle {

    private Circle circle;

    public CircularRectangle(Circle circle) {
        this.circle = circle;
    }

    // Some logic:
}

The purpose of the constructor is to keep reference to a circle.

Java does not allow multiinheritance,perhaps you can do in using composition :

CIRCULARRECTANGLE implements SHAPE .

CIRCULARRECTANGLE also contains an instance of CIRCLE and RECTANGLE .Then you implement the methods of CIRCULARRECTANGLE using this two instances according to your logic.

I would define 2 interfaces Circle and Rectangle. You classes will implement these interfaces. Then you can define interface CircularRectangle extending both interfaces. The tridr class CircularRectangle should have 2 instances cirlceInstance and rectangleInstance and delegate calls invoking necesary methods from the instances.

As java doesn't allow multiple inheritance, this is just not possible. You cannot let a class extend more than one superclass. Try using composition instead of inheritance.