Question

In Lab 5, you completed the MyRectangle class, which is a simple representation of a rectangle. Review Lab 5 before completing this lab and retrieve the MyRectangle class that you completed for this lab, since you will need it again in this lab. Before starting this lab, edit your MyRectangle class in the following way:

• change the declaration of your instance variables from private to protected

This will enable access of these variables by your MySquare subclass.

Here is my rectangle code :

// CS 401 Lab 05
// Fill in the indicated code sections to complete this class.  Then test it
// by compiling and executing Lab05.java.

public class MyRectangle
{
        // Declare instance variables here.  See toString() method below for names.

        public MyRectangle()
        {
                // Default constructor -- initialize all instance variables
                // to 0
        }

        public MyRectangle(int x, int y, int w, int h)
        {
                // Initialize instance variables based on parameters shown.
                // Be careful to get the order correct!
        }

        public int area()
        {
                // Return the area of this Rectangle
        }

        // I have written this method for you.  Note how a StringBuilder is
        // utilized, since (as we discussed in lecture) it can be modified
        // without having to create a new object each time (unlike a String).
        public String toString()
        {
                StringBuilder S = new StringBuilder();
                S.append("Width: " + width);
                S.append(" Height: " + height);
                S.append(" X: " + startX);
                S.append(" Y: " + startY);
                return S.toString();
        }

        public boolean isInside(int x, int y)
        {
                // This is the trickiest of the methods to write.  This should
                // return true if point (x,y) is anywhere within the borders of the
                // current MyRectangle (including the borders themselves).  Use a
                // pencil and paper to figure out how this can be determined with
                // just a few simple relational operations.
        }

        public void setSize(int w, int h)
        {
                // Update width and height as shown
        }

        public void setPosition(int x, int y)
        {
                // Update startX and startY as shown
        }

// rest of code

public class Lab05
{
        public static void testInside(MyRectangle R, int x, int y)
        {
                System.out.print("Point (" + x + "," + y + ")");
                if (R.isInside(x, y))
                        System.out.println(" is INSIDE " + R);
                else
                        System.out.println(" is OUTSIDE " + R);
        }

        public static void main(String [] args)
        {
                MyRectangle R1, R2, R3;

                R1 = new MyRectangle(100, 50, 80, 20);
                R2 = new MyRectangle();
                R3 = new MyRectangle(60, 60, 100, 100);
 
                // In Java, when Objects are printed (as shown below), the toString()
                // method is implicitly called.  Thus the statements below will call
                // toString() for each of the three MyRectangle objects
                System.out.println("R1: " + R1 + " Area: " + R1.area());
                System.out.println("R2: " + R2 + " Area: " + R2.area());
                System.out.println("R3: " + R3 + " Area: " + R3.area());

                int x1 = 120, y1 = 70;
                int x2 = 130, y2 = 110;

                // Verify with a pencil and paper which of these should be true and
                // which should be false.
                testInside(R1, x1, y1);
                testInside(R3, x1, y1);
                testInside(R1, x2, y2);
                testInside(R3, x2, y2);

                R1.setSize(120, 240);
                R3.setPosition(400, 350);
                testInside(R1, x2, y2);
                testInside(R3, x2, y2);
        }
}

What to Do?

In this lab, you will implement a new class with the following header:

public class MySquare extends MyRectangle

Your MySquare class should NOT have any new instance variables. If you think about it, you

will see that the instance variables already present in MyRectangle are sufficient. Note that

since you just changed the declarations of your instance variables to protected, a

subclass (MySquare) can have a direct access to the instance variables of the superclass

(MyRectangle). For this lab, you will need some new methods in your MySquare class as follows:

• public MySquare(int x, int y, int side): This is a constructor that allows new objects

to be created. x and y are the location coordinates and side is the side length.

• public MySquare(): This is a constructor that sets location (x,y) to (0,0) and side to 0.

• public String toString(): See output for effect of the toString() method.

• public void setSize(int w, int h): Redefine the setSize() method. This must be done

because the inherited version allows the width and height to difer but in a square they must

be the same. In this version, if the width and height are not the same, the method should

output a message and not change anything.

• public void setSide(int side): This is a new method that updates the size of the square.

Think about how this will be implemented using the existing inherited instance variables.

Your MySquare class must run with the Lab9.java program with no changes. To see how your

output should look, see the file lab9out.txt. Note that there are some methods that are utilized

in Lab9.java which are inherited and which you should not redefine in your MySquare class. See

details in the comments in Lab9.java.

// CS 0401 Lab 9 Driver Program
// Compile and run this program to test your MySquare class.
// Compare the output of your program with the provided file 
// lab8out.txt

public class Lab9
{
        // Note that this method has a MyRectangle parameter.   This should allow
        // it to work with the MyRectangle class or the MySquare class (because
        // MySquare ISA MyRectangle).  In other words, it only works with MySquare
        // because MySquare is a subclass of MyRectangle.  Finally, note that the
        // isInside() method can be used as is from MyRectangle -- you do not have
        // to redefine it for MySquare
        public static void showRec(MyRectangle R, int width, int height)
        {
                for (int i = 0; i < height; i++)
                {
                        for (int j = 0; j < width; j++)
                        {
                                if (R.isInside(i, j))
                                        System.out.print("+");
                                else
                                        System.out.print("-");
                        }
                        System.out.println();
                }
        }
        
        public static void main(String [] args)
        {
                MySquare S1, S2, S3;

                // Note the MySquare constructors.  You must write these.
                S1 = new MySquare(10, 20, 25);
                S2 = new MySquare();
                S3 = new MySquare(0, 0, 150);
 
                // The area() should be inherited -- you should not redefine it.  However
                // you must redefine the toString() method so that it outputs properly.
                System.out.println("S1: " + S1 + " Area: " + S1.area());
                System.out.println("S2: " + S2 + " Area: " + S2.area());
                System.out.println("S3: " + S3 + " Area: " + S3.area());

                showRec(S1, 80, 50);
                
                System.out.println();
                S1.setSide(15);                 // new method in MySquare class
                S1.setPosition(0, 0);   // inherited method
                
                System.out.println("S1: " + S1 + " Area: " + S1.area());
                showRec(S1, 80, 50);
                
                // The setSize() method is inherited from MyRectangle but as given it is
                // incorrect since the width and height can be assigned to different values.
                // Thus you should redefine the same method (with the same header) in the
                // MySquare class so that it makes the assignment only if the width and height
                // are the same (since the object is a square).  This is called method
                // overriding and we will discuss it soon in lecture.
                
                S1.setSize(20, 40);
                S1.setSize(20, 20);
                System.out.println("S1: " + S1 + " Area: " + S1.area());
        }
}

Answer 1

Solution:

MyRectangle.java

public class MyRectangle {
        // Declare instance variables here.  See toString() method below for names.
        protected double width;
        protected double height;
        protected double startX;
        protected double startY;

        public MyRectangle()
        {
            // Default constructor -- initialize all instance variables to 0
            width = 0;
            height = 0;
            startX = 0;
            startY = 0;
        }

        public MyRectangle(int x, int y, int w, int h)
        {
            // Initialize instance variables based on parameters shown.
            startX = x;
            startY = y;
            width = w;
            height = h;
        }

        public int area()
        {
            return (int)(width * height);
        }

        // I have written this method for you.  Note how a StringBuilder is
        // utilized, since (as we discussed in lecture) it can be modified
        // without having to create a new object each time (unlike a String).
        public String toString()
        {
            StringBuilder S = new StringBuilder();
            S.append("Width: " + width);
            S.append(" Height: " + height);
            S.append(" X: " + startX);
            S.append(" Y: " + startY);
            return S.toString();
        }

        public boolean isInside(int x, int y)
        {
            // This is the trickiest of the methods to write.  This should
            // return true if point (x,y) is anywhere within the borders of the
            // current MyRectangle (including the borders themselves).  Use a
            // pencil and paper to figure out how this can be determined with
            // just a few simple relational operations.

            if(x > startX && x < width && y > startY && y < height)
                return true;

            return false;
        }

        public void setSize(int w, int h)
        {
            // Update width and height as shown
            width = w;
            height = h;
        }

        public void setPosition(int x, int y)
        {
            // Update startX and startY as shown
            startX = x;
            startY = y;
        }
}

Lab05.java

public class Lab05 {
    public static void testInside(MyRectangle R, int x, int y)
    {
        System.out.print("Point (" + x + "," + y + ")");
        if (R.isInside(x, y))
            System.out.println(" is INSIDE " + R);
        else
            System.out.println(" is OUTSIDE " + R);
    }

    public static void main(String [] args)
    {
        MyRectangle R1, R2, R3;

        R1 = new MyRectangle(100, 50, 80, 20);
        R2 = new MyRectangle();
        R3 = new MyRectangle(60, 60, 100, 100);

        // In Java, when Objects are printed (as shown below), the toString()
        // method is implicitly called.  Thus the statements below will call
        // toString() for each of the three MyRectangle objects
        System.out.println("R1: " + R1 + " Area: " + R1.area());
        System.out.println("R2: " + R2 + " Area: " + R2.area());
        System.out.println("R3: " + R3 + " Area: " + R3.area());

        int x1 = 120, y1 = 70;
        int x2 = 130, y2 = 110;

        // Verify with a pencil and paper which of these should be true and
        // which should be false.
        testInside(R1, x1, y1);
        testInside(R3, x1, y1);
        testInside(R1, x2, y2);
        testInside(R3, x2, y2);

        R1.setSize(120, 240);
        R3.setPosition(400, 350);
        testInside(R1, x2, y2);
        testInside(R3, x2, y2);
    }
}

Output:

RI: Width: 80.0 Height: 20.0 X: ї00 0 Y: 50.0 Area : 1600 R2 : Width: 0.0 Height : 0,0 X: 0.0 Y: 0.0 Area: 0 R3: Width: 100.0 Height: 100.0 X: 60.0 Y: 60.0 Area 10000 Point (120,70) is OUTSIDE Width: 80.0 Height : 20.0 X: ї00 0 Y: 50.0 ↓ -Point (120,70) İS OUTSIDE Width: 100.0 Height: 100.0 X: 60.0 Y: 60.0 Point (130.110) is OUTSIDE Width: 80.0 Height: 20.0 X: ї00.0 Y: 50.0 Point (130,110) is OUTSIDE Width: 100.0 Height: 100.0 X: 60.0 Y: 60.0 Point (130,110) is OUTSIDE Width: 120.0 Height: 240.0 X: 1 Y: 50.0 Point (130,110) is OUTSIDE Width: 100.0 Height: 100.0 X: 400.0 Y: 350.0 匀

MySquare.java

public class MySquare extends MyRectangle{

    public MySquare(int x, int y, int side){
        this.startX = x;
        this.startY = y;
        this.width = side;
        this.height = side;
    }

    public MySquare(){
        startX = 0;
        startY = 0;
        width = 0;
        height = 0;
    }

    public String toString(){
        StringBuilder S = new StringBuilder();
        S.append("Width: " + width);
        S.append(" Height: " + height);
        S.append(" X: " + startX);
        S.append(" Y: " + startY);
        return S.toString();
    }

    public void setSize(int w, int h){
        if(w != h){
            System.out.printf("\n\n*****Value of 'w' and 'h' must be same******\n\n");
        }
        else {
            width = w;
            height = h;
        }
    }

    public void setSide(int side){
        width = side;
        height = side;
    }
}

Lab9.java

public class Lab9 {
    // Note that this method has a MyRectangle parameter.   This should allow
    // it to work with the MyRectangle class or the MySquare class (because
    // MySquare ISA MyRectangle).  In other words, it only works with MySquare
    // because MySquare is a subclass of MyRectangle.  Finally, note that the
    // isInside() method can be used as is from MyRectangle -- you do not have
    // to redefine it for MySquare
    public static void showRec(MyRectangle R, int width, int height)
    {
        for (int i = 0; i < height; i++)
        {
            for (int j = 0; j < width; j++)
            {
                if (R.isInside(i, j))
                    System.out.print("+");
                else
                    System.out.print("-");
            }
            System.out.println();
        }
    }

    public static void main(String [] args)
    {
        MySquare S1, S2, S3;

        // Note the MySquare constructors.  You must write these.
        S1 = new MySquare(10, 20, 25);
        S2 = new MySquare();
        S3 = new MySquare(0, 0, 150);

        // The area() should be inherited -- you should not redefine it.  However
        // you must redefine the toString() method so that it outputs properly.
        System.out.println("S1: " + S1 + " Area: " + S1.area());
        System.out.println("S2: " + S2 + " Area: " + S2.area());
        System.out.println("S3: " + S3 + " Area: " + S3.area());

        showRec(S1, 80, 50);

        System.out.println();
        S1.setSide(15);                 // new method in MySquare class
        S1.setPosition(0, 0);   // inherited method

        System.out.println("S1: " + S1 + " Area: " + S1.area());
        showRec(S1, 80, 50);

        // The setSize() method is inherited from MyRectangle but as given it is
        // incorrect since the width and height can be assigned to different values.
        // Thus you should redefine the same method (with the same header) in the
        // MySquare class so that it makes the assignment only if the width and height
        // are the same (since the object is a square).  This is called method
        // overriding and we will discuss it soon in lecture.

        S1.setSize(20, 40);
        S1.setSize(20, 20);
        System.out.println("S1: " + S1 + " Area: " + S1.area());
    }
}

Output:

S1: Width: 25.0 Height: 25.0 X: 10.0 Y: 20.0 Area: 625
S2: Width: 0.0 Height: 0.0 X: 0.0 Y: 0.0 Area: 0
S3: Width: 150.0 Height: 150.0 X: 0.0 Y: 0.0 Area: 22500
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S1: Width: 15.0 Height: 15.0 X: 0.0 Y: 0.0 Area: 225
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-++++++++++++++-----------------------------------------------------------------
-++++++++++++++-----------------------------------------------------------------
-++++++++++++++-----------------------------------------------------------------
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*****Value of 'w' and 'h' must be same******

S1: Width: 20.0 Height: 20.0 X: 0.0 Y: 0.0 Area: 400