Name: dk106046 Date: 10/01/2003

When Unicode character list is displayed using a sample Java program under Japanese environment, too much CPU time is used.

The CharacterList program accepts two option parameter. The first one is the interval of screen updates in millseconds and the second one is number of Unicode characters to be displayed in order.

If the program was invoked with:
java CharacterList 500 1000
it will display only first 1000 characters of CJK Unified Ideographs and the CPU usage is very low.

If the program was invoked with:
java CharacterList 500 2000
it will display first 2000 characters and CPU usage is almost 100%.

/*
 * CharacterList.java
 */

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class CharacterList extends JPanel {

    public CharacterList() {
        setPreferredSize(new Dimension(WIDTH, HEIGHT));
        font = new Font("Monospaced", Font.PLAIN, 16);
        codePoint = codePointLow;
        timer = new Timer(interval,
            new ActionListener() {
                public void actionPerformed(ActionEvent e){
                    repaint();
                }
            });
        timer.start();
    }
    
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        
        this.g = g;

        int panelWidth = getWidth();
        int panelHeight = getHeight();

        g.setFont(font);
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, panelWidth, panelHeight);
        g.setColor(Color.BLACK);

        if (stringLength == 0) {
            FontMetrics fm = g.getFontMetrics();
            width = fm.charWidth(FULL_WIDTH_ZERO);
            height = fm.getHeight();
        }
        
        stringLength = panelWidth / width;
        
        for (int y = height; y < panelHeight; y += height)
            g.drawString(getString(), 0, y);
    }
    
    public String getString() {
        char[] ca = new char[stringLength];
        
        for (int i =0; i < stringLength; ++i) {
            ca[i] = (char)codePoint++;
            if (codePoint > codePointHigh)
                codePoint = codePointLow;
        }
        
        return new String(ca);
    }
    
    public static void main(String[] args) {
        interval = DEFAULT_INTERVAL;
        try {
            interval = Integer.parseInt(args[0]);
            if (args.length > 1) {
                numberOfCharacters = Integer.parseInt(args[1]);
                codePointHigh = codePointLow + numberOfCharacters;
            }
        } catch (Exception e) {
        }
        
        System.out.println("redraw interval (msec) = " + interval);
        if (numberOfCharacters > 0)
            System.out.println("number of characters to be displayed in the list = "
                + numberOfCharacters);
            
        JFrame frame = new JFrame(TITLE);
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        
        frame.setContentPane(new CharacterList());
        frame.pack();
        frame.setResizable(false);
        frame.setVisible(true);
    }
    
    private Font font;
    private int codePoint;
    private int width, height, stringLength;
    
    private Timer timer;
    private Graphics g;

    private static final String TITLE = "CharacterList";
    private static final int WIDTH = 400;
    private static final int HEIGHT = 400;
    
    private static final char FULL_WIDTH_ZERO = '\uff10';

    private static final int CODE_POINT_LOW = 0x4e00;
    private static final int CODE_POINT_HIGH = 0x9fff;

    private static final int DEFAULT_INTERVAL = 500;

    private static int interval;
    private static int numberOfCharacters;
    private static int codePointLow = CODE_POINT_LOW;
    private static int codePointHigh = CODE_POINT_HIGH;
}

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