85 lines
2.2 KiB
Java
85 lines
2.2 KiB
Java
// patterns/BoxObserver.java
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// (c)2021 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// Demonstration of the Observer pattern using
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// Java's built-in observer classes.
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// {ExcludeFromGradle} // Won't work under WSL2
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import javax.swing.*;
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import java.awt.*;
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import java.awt.event.*;
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import java.util.*;
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import onjava.*;
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import onjava.MouseClick;
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@SuppressWarnings("deprecation")
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class Boxes extends JFrame {
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Observable notifier = new Observable() {
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@Override
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public void notifyObservers(Object b) {
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setChanged();
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super.notifyObservers(b);
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}
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};
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public Boxes(int grid) {
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setTitle("Demonstrates Observer pattern");
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Container cp = getContentPane();
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cp.setLayout(new GridLayout(grid, grid));
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for(int x = 0; x < grid; x++)
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for(int y = 0; y < grid; y++)
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cp.add(new Box(x, y, notifier));
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setSize(500, 400);
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setVisible(true);
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setDefaultCloseOperation(DISPOSE_ON_CLOSE);
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}
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}
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@SuppressWarnings("deprecation")
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class Box extends JPanel implements Observer {
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int x, y; // Location in grid
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Color color = COLORS[
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(int)(Math.random() * COLORS.length)
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];
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static final Color[] COLORS = {
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Color.black, Color.blue, Color.cyan,
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Color.darkGray, Color.gray, Color.green,
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Color.lightGray, Color.magenta,
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Color.orange, Color.pink, Color.red,
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Color.white, Color.yellow
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};
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Box(int x, int y, Observable notifier) {
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this.x = x;
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this.y = y;
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notifier.addObserver(this);
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addMouseListener((MouseClick)
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e -> notifier.notifyObservers(Box.this));
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}
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@Override public void paintComponent(Graphics g) {
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super.paintComponent(g);
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g.setColor(color);
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Dimension s = getSize();
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g.fillRect(0, 0, s.width, s.height);
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}
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@Override
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public void update(Observable o, Object arg) {
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Box clicked = (Box)arg;
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if(nextTo(clicked)) {
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color = clicked.color;
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repaint();
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}
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}
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private boolean nextTo(Box b) {
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return Math.abs(x - b.x) <= 1 &&
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Math.abs(y - b.y) <= 1;
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}
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}
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public class BoxObserver {
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public static void main(String[] args) {
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int grid = 8;
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if(args.length > 0)
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grid = Integer.parseInt(args[0]);
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new Boxes(grid);
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}
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}
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