如何在Java Applet中创建图形实例

Question

We've just learned how to create our own class, and this particular assignment we had to work with graphics. We had to draw a crayon, and then create a test program where there are 5 crayons lined up next to one another (so we just change the color and x,y of each one). I know how to change the color and x,y coords, but my question is...

how do I 'print' each crayon? Yes, it's an applet and yes I know I need a .html file. But what exactly goes in the test program in order for the crayon to show up when I run the .html file? I've run non-applets before in test programs using System.out.println , but never any graphics. Would it just be System.out.println(Crayon); ?

Also, how do I get multiple crayons? I'm assuming it's Crayon crayons = new Crayon ;, and then the next one might be 'Crayon crayons2 = new Crayons;`? I'm not sure.

The x,y coordinates need to be modified w/each crayon, but the UML for the assignment told me not to make them instance variables but instead to put it in 'public void paint (Graphics g, int x, int y)'. What I have so far for the test program (may or may not be correct):

import javax.swing.JApplet;
import java.awt.*;

public class BoxOfCrayons extends JApplet {
   Crayon first = new Crayon (Color.red, 50, 250)

Answer 1

Start by having a read through 2D Graphics .

Basically, you will need to create some kind of list of Cryon s. This can either be a Collection or array, depending on what you know. I would personally use a ArrayList as it's flexible and easy to use, but doesn't suffer from the same constraints as an array.

Next, create you're self a custom component (ie BoxOfCryons ) which extends from JPanel . Override this classes paintComponent method. Within this method, run through the list of Cryon s and paint each one, incrementing the x offset by the width of the last Cryon .

protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g.create();
    int x = 0;
    int y = 0;
    for (Crayon crayon : cryons) {
        crayon.paint(g2d, x, y);
        x += crayon.getWidth();
    }
    g2d.dispose();
}

Create yourself a new class that extends from JApplet . In it's init method, set the applets layout manager to BorderLayout and add an instance of the BoxOfCryons class to it.