Chapter 9, Problem 12E

Explanation of Solution

Adding “equals()” method to “Rectangle”, “Circle” and “Triangle” class:

//Definition of method equals() for Rectangle class

public boolean equals(Object obj)

{

    //Check whether "obj" is the instance of Rectangle

    if (obj instanceof Rectangle)

    {

        //Create an object "rectVal" to Rectangle

        Rectangle rectVal = (Rectangle) obj;

        //Return the width and height

return width == rectVal.width && height == rectVal.height;

    }

    //Otherwise, the width and height is not valid

    else

    {

        //Then return the value false

        return false;

    }

}

//Definition of method equals() for Circle Class

public boolean equals(Object obj)

{

    //Check whether "obj" is the instance of Cicle

    if (obj instanceof Circle)

    {

        //Create an object "cirVal" to Circle

        Rectangle cirVal = (Circle) obj;

        //Assign and return the radisu

        return radius == cirVal.radius;

    }

    //Otherwise, the value of radius not valid

    else

    {

        //Then return the value false

        return false;

    }

}

//Definition of method equals() for Triangle class

public boolean equals(Object obj)

{

    //Check whether "obj" is the instance of Triangle

    if (obj instanceof Triangle)

    {

        //Create an object "triVal" to Rectangle

        Triangle triVal = (Triangle) obj;

        //Assign and return the a, b and c

return a == triVal...