The following Java program draws a simple house using basic shapes

Practical Exercise 1 House

The following Java program draws a simple house using basic shapes.

The shapes are drawn using paint(Graphics g ) which is one of the standard methods used in Java.
import java.awt.*;

import java.applet.*;

// Program to draw a house

public class House extends Applet

{

public void paint(Graphics g)

{

// Draw the roof

g.setColor(Color.red);

int xs[] = {100,160,220};

int ys[] = {100,50,100};

Polygon poly=new Polygon(xs,ys,3);

g.fillPolygon(poly);

// Draw the body of house

g.setColor(Color.blue);

g.fillRect(100,100,120,120);

// draw the door

g.setColor(Color.white);

g.fillRect(145,160,30,60);

// draw sun

g.setColor(Color.yellow);

g.fillOval(240,30,50,50);

//draw chimney

g.setColor(Color.black);

g.fillRect(120,55,10,30);

}

}

Explanatory Notes on the “House” class:

Packages

The Java Applications Programming Interface (API) contains a large number of programming features grouped into “packages” of related features. When you write a program or class in Java you must import those packages which are used in the class.

The java.applet package is used in all classes in this course.

The java.awt package is used to create the graphics used in the applet windows.
Class

We will have a lot more to say about classes in this course. For the time being, you can regard a class as a program, and every class that you write will begin with the line:

public class extends Applet

paint( )

A method is a section of code that does a particular job in a class. Methods (in Object Oriented languages) are essentially the same as procedures and functions in other languages. They enable you to break up a long piece of code into smaller more manageable modules. These methods can be used many times in the original class and can be used in other classes.

One of the standard methods used in java applets is the paint( ) method. This is responsible for painting graphics and text into the applet window.
If you want to use the paint method you always begin with the line:

public void paint (Graphics g)

Drawing Shapes

Most graphics operations in Java are built into Java's Graphics class. This Graphics class is part of the java.awt package, so if your applet does any painting you will need to import that class at the beginning of your program
ie import java.awt.*
Now you have access to a great variety of graphics operations. For example:
g.drawRect(x, y, length, width) draws an outline of a rectangle

g.fillRect(x, y, length, width) fills a rectangle in with colour

g.drawRoundRect(x, y, length, width, cwidth,cheight)

draws an outline of a rectangle with rounded corners

g.fillRoundRect(x, y, length, width, cwidth, cheight)

fills in a rectangle with rounded corners with colour

g.drawOval((x, y, length, width) draws an outline of an oval or a circle

g.fillOval((x, y, length, width) fills ovals or circles with colour

g.drawLine(x1,y1,x2,y2) draws a line from (x1,y1) to (x2,y2)

setBackground(Color.white) change background colour (default is grey)

To find out more about colours you can look up the Java help menu under

http://java.sun.com/j2se/1.4.1/docs/api/index.html
Colors (Note American spelling of Colours!)

Standard colors provided in java are:

Colours	RGB Codes	Colours	RGB Codes
Color.black	0, 0, 0	Color.gray	128, 128, 128
Color.white	255, 255, 255	Color.lightGray	192, 192, 192
Color.red	255, 0, 0	Color.darkGray	64, 64, 64
Color.orange	255, 200, 0	Color.cyan	0, 255, 255
Color.yellow	255, 255, 0	Color.blue	0, 0, 255
Color.magenta	255, 0, 255	Color.green	0, 255, 0
Color.pink	255, 175, 175

To use these in paint( ) you use a statement such as:

g.setColor(Color.green);

Window Coordinates

When you draw a graphics object on the applet window, you must specify its coordinates.

The top left corner of an applet window has coordinates (0,0).

Position from the top left is measured in pixels, and a typical window might be 800 pixels wide by 600 pixels high, so that its bottom right has coordinates (800, 600).

For example the following rectangle (width = 200, length = 100) would have coordinates as shown

(0,0) (200,0)

(0,100) (200,100)

Exercise

C Standard

1. 
   Create a new eclipse project called ‘Prac_1’, and create a new class file inside this project called ‘House’.
   
2. 
   Type in the code above and get the program working. (Remember to click ‘Run As Applet’)
   
3. 
   Improve your house by adding 2 windows, making the door black and the roof magenta.
   

B Standard

Add at least 3 extra features to your house.

A Standard

Place the house in a scene. Eg. Sky & clouds, grass, trees, fence etc.

Rosny College 2009 Page of