Spring 2009 Programming Fundamentals I

Java Programming

XuanTung Hoangtung_hx@icu.ac.kr

Lecture No. 18

Java GUI

1. Introduction2. Java Graphics

GUI in a nutshell

Other topics: Drawing Capabilities

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Drawing on a panel Sometimes it is necessary to paint on a GUI

component For example: Paint on a JPanel, paint on a JButton, …

How to paint on a GUI component? Create a subclass of the component (inheritance) Override paintComponent(Graphics g)

method The argument g is the object that provide drawing capabilities

Use the object g to paint Frequently used methods: getClipBounds(),

setColor(), getColor(), clearRect(), drawRect(), fillRect(), drawLine(), drawOval()

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Example: Drawing on a Panel

Create our own panel class by extending JPanel Override paintComponent() method and put our

drawing code there Create our own frame and use our panel class as a

Swing component

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Our own panel class

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Graphics class: Class that represents “graphic contexts”

The area that paintComponent() will draw on Control font styles/line patterns/fill patterns/colors Provide drawing support methods

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Getting drawing area from Graphics object

Rectangle class

Rectangle r specifies drawing area of Graphics object g in current drawing context coordinate system

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Drawing using Graphics object

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Put our drawing panel into a frame and show the frame NOTE: setLayout before adding drawing panel

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Output

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We can add more GUI components to control drawing

How ?

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Example: Make a snake that runs We will make a snake that runs across a panel Solution:

A snake = a horizontal line = a point (x, y) (the head) , a length, and a direction

We use a timer, after each timer event we change position of the head and repaint the snake on a panel

(x, y)

length

LEFT = 0 RIGHT = 1

DOWN = 2

UP= 3

dir

(0, 0)

(MAXX, MAXY)

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Render and image on a panel Import java.awt.image.* Import javax.imageio.* Create a BufferedImage object using static method read of ImageIO

class

BufferedImage img = ImageIO.read(new FileInputStream(“Image.jpg” ));

Draw the image with drawImage() method of class Graphics

g.drawImage(img, x, y, width, height, null);

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Example: Display cards on Panel