Script for live demo part of Day 7 and 8 SWING Intro for CSSE 220
Make a new project (FirstGraphics) and a new class (FirstGraphics).
import javax.swing.JFrame;
Why javax? When first introduced, Swing was an extension to Java, not part of the standard distribution.
static final int FRAME_WIDTH = 300;
static final int FRAME_HEIGHT = 400;
We don't want to use magic numbers.
Now add each of the following lines, explaining as we go (mainly explain what happens if we don't do them)
JFrame frame = new JFrame(); Create the window. Unlike in ZelleGraphics, the window is not
automatically displayed.
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT); If we leave this out, both height and width will be zero, so we
won't see a window,
frame.setTitle("First Graphics"); If we leave this out, the window will not have a title
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); If we leave this out, clicking the window's Close button will not
kill the program. Note that EXIT_ON_CLOSE is a (static)
constant from the JFrame class.
frame.setVisible(true); If we leave this out, the window will not display
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Run it and see the empty window.
Quiz Question 7
This is a good "boilerplate" for getting a GUI program
up and going.
Question: How could we modify this code to display
two windows?
Do it.
Now we want to display a couple of rectangles
in the window. We need a new class that extends JComponent.
Call it FirstGraphicsComponent Superclass: javax.swing.JComponent.
(Do not type in all of the imports. Let Eclipse add them
as needed (click the red X and choose the import option)
public void paintComponent(Graphics g) {
This is the method we always write to paint a component.
But we don't ever need to call it. It gets called when needed.
Quiz Question 8
Where does the g come from? We don't need to create it.
Add the line to paintComponent:
g.drawRect(20, 20,75, 100);
Then add these lines to the FirstGraphics class:
FirstGraphicsComponent component =
new FirstGraphicsComponent();
frame.add(component);
import javax.swing.JFrame;
public class FirstGraphics{
static final int FRAME_WIDTH = 300;
static final int FRAME_HEIGHT = 400;
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
frame.setTitle("First Graphics");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import javax.swing.JPanel;
import javax.swing.JComponent;
/**
A component that draws two rectangles.
*/
public class FirstGraphicsComponent extends JComponent {
public void paintComponent(Graphics g) {
// Recover Graphics2D
Graphics2D g2 = (Graphics2D) g;
// Construct a rectangle and draw it
Rectangle box = new Rectangle(5, 10, 20, 30);
g2.draw(box);
// Move rectangle 15 units right and 25 units down
box.translate(15, 25);
// Draw moved rectangle
g2.draw(box);
}
}
