Java

OOP GUIDE / WORK

RECTANGLE CLASS 2

Topics

• Constructors, constructor overloading, constructor chaining
  
  

TASK – PART 1 – SETUP

Copy the follow class into your IDE (Eclipse).

public class Rectangle

{

public double x, y; //x and y of top left corner

public double w, h; //width and height

public String colour; //ie: "pink" or "blue"

public String toString()

{

String s = "Top left corner: (" + x + "," + y + "), ";

s = s + "Width: " + w + ", Height: " + h + ", ";

s = s + "Colour: " + colour;

return s;

}

public double area()

{

return w * h;

}

}

TASK – PART 2 – ADDITIONS

Add the following constructors. Notice that we can have multiple constructors as long as each one has a different parameter list. This is called constructor overloading.

CONSTRUCTORS (6)

· It has a constructor that gets five parameters, one for each instance variable.

· It has a constructor that gets four parameters, one for each of the numeric instance variables. All of these rectangles will be “black”.

· It has a constructor that gets four parameters. It will construct rectangles with an equal width and height – so squares really. Two of the parameters are for x and y, one that is the side length of the square and one that is for colour.

· It has a constructor that gets three parameters. This constructor is the same as the previous one but doesn’t get a colour as it create black rectangles.

· It has a constructor that gets three parameters. The first two parameters are for x and y. The last parameter is for the colour. The values of w and h will always be set to 1.

· It has a constructor that gets two parameters for x and y. The value of w and h are both set to 1. The value of colour is “black”.

TASK – PART 3 – CONSTRUCTOR CHAINING

Constructor chaining is when one constructor calls another constructor. This is done by using:

this(parameters);

on the very first line inside the constructor.

Alter your program above so that Constructors #2 to 6 all use constructor chaining. So they will all call the first constructor.

TASK – 4 – TESTING YOUR RECTANGLE CLASS

Create a class called RectangleTester and follow the following steps:

• Add a main function to the class.
  
  
• Inside main, create six different rectangle objects making use of the six different constructors.
  
  
• Output each rectangle object to screen (making use of its toString() method)