CS125: Introduction to Programming Principles

Lab 07

PLEASE NOTE: All lab exercises are due by Monday June 23rd at 10:00am.
1. Download Files
2. What You Should Know
3. Create a Class
4. Request Lab Solutions

Download Files

Download the L07.zip file and extract the files to your cs125 folder in your home directory. You will use these files to complete this week's lab exercises.

What You Should Know

This lab covers objects. A quick overview is given here.

Often it is useful to create a new class whose instances make it easier to use instances of some previously-existing class. The Scanner class you have been using is an example of this--it makes it way easier to use the InputStream object System.in to read input from the keyboard.

Your are going to create a class called FancyBoard that's able to draw rectangles, as well as drawing lines and pegs, on a 2-D Board object. Here's the class diagram for FancyBoard.

- Board myBoard

+            FancyBoard( int rows, int cols )
+ void       displayMessage( String theMessage )
+ void       drawLine( int row1, int col1, int row2, int col2 )
+ void       drawRectangle( Coordinate topLeft, Coordinate bottomRight )
+ Coordinate getClick()
+ int        getColumns()
+ int        getRows()
+ void       putPeg( String theColour, int row, int col )
+ void       removeLine( int row1, int col1, int row2, int col2 )
+ void       removePeg( int row, int col )
+ void       removeRectangle( Coordinate topLeft, Coordinate bottomRight )

Begin by creating a file named FancyBoard.java with the appropriate opening text "public class FancyBoard {" and closing text "}".

Add a declaration for the instance variable myBoard.

Add code for the FancyBoard constructor. It will need to create a Board object, and save its address in the instance variable myBoard.

Create a method definition in FancyBoard for each 2-d method in the Board class shown in the above class diagram. (They're all in black text.) These methods should simply call the corresponding board object's method, passing on the arguments supplied, and returning the value that the board method returns, if there is one. For example, the implementations of displayMessage(...) and getClick() would look like this:

    public void displayMessage( String msg ) {
        this.myBoard.displayMessage( msg );
    }
    public Coordinate getClick() {
        return this.myBoard.getClick();
    }

You can simply type this code into your FancyBoard.java file--it does just what you want. Then do something analogous to define drawLine(...), getColumns(), getRows(), putPeg(...), and removePeg().

Finally, add definitions for the new methods drawRectangle(...) and removeRectangle(...) that use the board object's drawLine(...) and removeLine(...) methods to draw and remove a rectangle from the board.

That's it! You can use the file UsingFancyBoard.java to test your implementation of FancyBoard. When you run it, you should first see the board that appears bottom-left; then click on the board, and the red peg, lines, and rectangle should be removed, resulting in the board you see bottom-right.

Submit the code for FancyBoard.java here.

You are given the Rectangle.class (i.e., the compiled version of the Rectangle.java file), which has the following class diagram:

+int height
+int width

+Rectangle(int newHeight, int newWidth)
+setHeight(int newHeight)
+setWidth(int newWidth)
+int getHeight()
+int getWidth()
+int computeArea()

It is worth noting that the pre and post conditions for setHeight are

// PRE:  none
// POST:  sets this.height to be the provided value, if that value is >0
//        otherwise,  do not change the height

Also, the constructor ensures that all non-positive numbers are treated as 1 (since a Rectangle with negative width/height doesn't make sense). You can try the methods out if you wish to verify this.

Open the file WreckedRectangle.java. Using what you know about public and private, along with the Rectangle class provided to you, make a modification to the WreckedRectangle.java file such that the Rectangle has a negative height. You may only add one line of code and you may not use any of the methods in Rectangle.java (since they won't help you). (Note: Rectangle.class has to be in the same directory as your WreckedRectangle.java)

Submit ALL the code for WreckedRectangle.java here.

Request Lab Solutions

If you request solutions for this lab you will be sent an email that contains your answers as well as the expected answers. The email will be sent out to all interested students once the usual deadline for completing the exercises has passed for all students.