模擬時鐘工作，但秒重繪

Question

我做了一個模擬時鐘和它的工作，但當刪除filloval（背景）秒針不斷重複自己，但是當我添加filloval它工作。但我不希望那裏的背景。由於

這裏是代碼

import java.awt.Color; 
import java.awt.Font; 
import java.awt.Graphics; 
import java.text.SimpleDateFormat; 
import java.util.Date; 
import java.util.Locale; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 

public class Clock extends JPanel implements Runnable { 

    Thread thread = null; 
    SimpleDateFormat formatter = new SimpleDateFormat("s", Locale.getDefault()); 
    Date currentDate; 
    int xcenter = 175, ycenter = 175, lastxs = 0, lastys = 0, lastxm = 0, lastym = 0, lastxh = 0, lastyh = 0; 

    private void drawStructure(Graphics g) { 
     g.setFont(new Font("TimesRoman", Font.BOLD, 20)); 
     g.setColor(Color.black); 
//g.fillOval(xcenter - 150, ycenter - 150, 300, 300); 
     g.setColor(Color.blue); 
     g.setColor(Color.green); 
     g.drawString("9", xcenter - 145, ycenter + 0); 
     g.drawString("3", xcenter + 135, ycenter + 0); 
     g.drawString("12", xcenter - 10, ycenter - 130); 
     g.drawString("6", xcenter - 10, ycenter + 145); 
    } 

    public void paint(Graphics g) { 
     int xhour, yhour, xminute, yminute, xsecond, ysecond, second, minute, hour; 
     drawStructure(g); 
     currentDate = new Date(); 
     formatter.applyPattern("s"); 
     second = Integer.parseInt(formatter.format(currentDate)); 
     formatter.applyPattern("m"); 
     minute = Integer.parseInt(formatter.format(currentDate)); 
     formatter.applyPattern("h"); 
     hour = Integer.parseInt(formatter.format(currentDate)); 
     xsecond = (int) (Math.cos(second * 3.14f/30 - 3.14f/2) * 120 + xcenter); 
     ysecond = (int) (Math.sin(second * 3.14f/30 - 3.14f/2) * 120 + ycenter); 
     xminute = (int) (Math.cos(minute * 3.14f/30 - 3.14f/2) * 100 + xcenter); 
     yminute = (int) (Math.sin(minute * 3.14f/30 - 3.14f/2) * 100 + ycenter); 
     xhour = (int) (Math.cos((hour * 30 + minute/2) * 3.14f/180 - 3.14f/2) * 80 + xcenter); 
     yhour = (int) (Math.sin((hour * 30 + minute/2) * 3.14f/180 - 3.14f/2) * 80 + ycenter); 
// Erase if necessary, and redraw 
     g.drawLine(xcenter, ycenter, xsecond, ysecond); 
     g.setColor(Color.red); 
     g.drawLine(xcenter, ycenter - 1, xminute, yminute); 
     g.drawLine(xcenter - 1, ycenter, xminute, yminute); 
     g.setColor(Color.green); 
     g.drawLine(xcenter, ycenter - 1, xhour, yhour); 
     g.drawLine(xcenter - 1, ycenter, xhour, yhour); 
     lastxs = xsecond; 
     lastys = ysecond; 
     lastxm = xminute; 
     lastym = yminute; 
     lastxh = xhour; 
     lastyh = yhour; 
    } 

    public void start() { 
     if (thread == null) { 
      thread = new Thread(this); 
      thread.start(); 
     } 
    } 

    public void stop() { 
     thread = null; 
    } 

    public void run() { 
     while (thread != null) { 
      try { 
       Thread.sleep(100); 
      } catch (InterruptedException e) { 
      } 
      repaint(); 
     } 
     thread = null; 
    } 

    public void update(Graphics g) { 
     paint(g); 
    } 

    public static void main(String args[]) { 
     JFrame frame = new JFrame(); 
     Color c = new Color(118, 73, 190); 
     frame.setBackground(c); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.setBounds(0, 0, 400, 400); 
     Clock clock = new Clock(); 
     frame.getContentPane().add(clock); 
     frame.setVisible(true); 
    } 
} 

Answer 1

取而代之的首要paint()，Swing程序應該重寫paintComponent()。另外，調用super.paintComponent()來避免這種渲染artifact。在這個相關的example中說明了類似的問題。一些額外的意見：

• 擺動程序應該構造和更新event dispatch thread。

• 使用Swing timer更新顯示。

爲試：

import java.awt.EventQueue; 
import java.awt.Font; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.RenderingHints; 
import java.awt.event.ActionEvent; 
import java.text.SimpleDateFormat; 
import java.util.Date; 
import java.util.Locale; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.Timer; 

//* @see https://stackoverflow.com/a/26213625/230513 */ 
public class Clock extends JPanel { 

    private Timer t = new Timer(1000, (ActionEvent e) -> { 
     repaint(); 
    }); 
    private SimpleDateFormat formatter = new SimpleDateFormat("s", Locale.getDefault()); 
    private Date currentDate; 
    private int xcenter = 175, ycenter = 175, lastxs = 0, lastys = 0, lastxm = 0, lastym = 0, lastxh = 0, lastyh = 0; 

    private void drawStructure(Graphics g) { 
     g.setFont(new Font("TimesRoman", Font.BOLD, 20)); 
     g.drawString("9", xcenter - 145, ycenter + 0); 
     g.drawString("3", xcenter + 135, ycenter + 0); 
     g.drawString("12", xcenter - 10, ycenter - 130); 
     g.drawString("6", xcenter - 10, ycenter + 145); 
    } 

    @Override 
    public void paintComponent(Graphics g) { 
     super.paintComponent(g); 
     Graphics2D g2d = (Graphics2D) g; 
     g2d.setRenderingHint(
       RenderingHints.KEY_ANTIALIASING, 
       RenderingHints.VALUE_ANTIALIAS_ON); 
     int xhour, yhour, xminute, yminute, xsecond, ysecond, second, minute, hour; 
     drawStructure(g); 
     currentDate = new Date(); 
     formatter.applyPattern("s"); 
     second = Integer.parseInt(formatter.format(currentDate)); 
     formatter.applyPattern("m"); 
     minute = Integer.parseInt(formatter.format(currentDate)); 
     formatter.applyPattern("h"); 
     hour = Integer.parseInt(formatter.format(currentDate)); 
     xsecond = (int) (Math.cos(second * 3.14f/30 - 3.14f/2) * 120 + xcenter); 
     ysecond = (int) (Math.sin(second * 3.14f/30 - 3.14f/2) * 120 + ycenter); 
     xminute = (int) (Math.cos(minute * 3.14f/30 - 3.14f/2) * 100 + xcenter); 
     yminute = (int) (Math.sin(minute * 3.14f/30 - 3.14f/2) * 100 + ycenter); 
     xhour = (int) (Math.cos((hour * 30 + minute/2) * 3.14f/180 - 3.14f/2) * 80 + xcenter); 
     yhour = (int) (Math.sin((hour * 30 + minute/2) * 3.14f/180 - 3.14f/2) * 80 + ycenter); 
     g.drawLine(xcenter, ycenter, xsecond, ysecond); 
     g.drawLine(xcenter, ycenter - 1, xminute, yminute); 
     g.drawLine(xcenter - 1, ycenter, xminute, yminute); 
     g.drawLine(xcenter, ycenter - 1, xhour, yhour); 
     g.drawLine(xcenter - 1, ycenter, xhour, yhour); 
     lastxs = xsecond; 
     lastys = ysecond; 
     lastxm = xminute; 
     lastym = yminute; 
     lastxh = xhour; 
     lastyh = yhour; 
    } 

    public void start() { 
     t.start(); 
    } 

    public void stop() { 
     t.stop(); 
    } 

    public static void main(String args[]) { 
     EventQueue.invokeLater(() -> { 
      JFrame frame = new JFrame(); 
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
      frame.setBounds(0, 0, 400, 400); 
      Clock clock = new Clock(); 
      frame.getContentPane().add(clock); 
      frame.setVisible(true); 
      clock.start(); 
     }); 
    } 
}