在JFrame上繪製點的總距離

Question

我想打印總距離，就像你可以看到我有page.drawString（「Distance：」+ fmt.format（length），10,15）;在我的代碼中。但是這僅增加了從點1到點2的長度。我希望它繼續添加例如我畫一條線從點1到點2有30的距離，然後再次畫了一條線從點1到點2有20的距離，所以我的drawString應該顯示爲50結果。

import javax.swing.JPanel; 
import java.awt.*; 
import java.awt.event.*; 
import java.text.DecimalFormat; 

public class RubberLinesPanel extends JPanel { 

    private Point current = null, point2 = null; 
    private double length; 
    private DecimalFormat fmt; 

    public RubberLinesPanel() { 
     LineListener listener = new LineListener(); 
     addMouseListener(listener); 
     addMouseMotionListener(listener); 
     setBackground(Color.black); 
     setPreferredSize(new Dimension(400, 200)); 
     fmt = new DecimalFormat("0.##"); 
    } 

    public void paintComponent(Graphics page) { 
     super.paintComponent(page); 
     page.setColor(Color.yellow); 
     if (current != null && point2 != null) 
     page.drawLine(current.x, current.y, point2.x, point2.y); 
     page.drawString("Distance: " + fmt.format(length), 10, 15); 
    } 

    private class LineListener implements MouseListener, MouseMotionListener { 

     public void mousePressed(MouseEvent event) { 
      current = event.getPoint(); 
     } 
     //-------------------------------------------------------------- 
     // Gets the current position of the mouse as it is dragged and 
     // redraws the line to create the rubberband effect. 
     //-------------------------------------------------------------- 
     public void mouseDragged(MouseEvent event) { 
      point2 = event.getPoint(); 
      length = Math.sqrt(Math.pow((current.x - point2.x), 2) + 
      Math.pow((current.y - point2.y), 2)); 
      repaint(); 
     } 
     //-------------------------------------------------------------- 
     // Provide empty definitions for unused event methods. 
     //-------------------------------------------------------------- 
     public void mouseClicked(MouseEvent event) {} 
     public void mouseReleased(MouseEvent event) {} 
     public void mouseEntered(MouseEvent event) {} 
     public void mouseExited(MouseEvent event) {} 
     public void mouseMoved(MouseEvent event) {} 
    } 
} 

Answer 1

的解決方案是簡單地給你的類double totalDistance字段，它初始化爲0，然後計算後立即每個計算的長度添加到totalDistance字段。

public class RubberLinesPanel extends JPanel { 
    private Point current = null, point2 = null; 
    private double length; 
    private double totalDistance = 0.0; // ***** add this ***** 
    private DecimalFormat fmt; 

    public RubberLinesPanel() { 
     // .... etc ..... 
    } 

    public void paintComponent(Graphics page) { 
     super.paintComponent(page); 
     page.setColor(Color.yellow); 
     if (current != null && point2 != null) 
      page.drawLine(current.x, current.y, point2.x, point2.y); 
     page.drawString("Distance: " + fmt.format(length), 10, 15); 

     // draw totalDistance here // ************ draw it here 
    } 

    private class LineListener implements MouseListener, MouseMotionListener { 

     public void mousePressed(MouseEvent event) { 
      current = event.getPoint(); 
     } 

     public void mouseDragged(MouseEvent event) { 
      point2 = event.getPoint(); 
      length = Math.sqrt(Math.pow((current.x - point2.x), 2) 
        + Math.pow((current.y - point2.y), 2)); 
      totalDistance += length; // ******* calculate it here 
      repaint(); 
     } 

還是我過分簡化了你的問題，因爲這個解決方案看起來太簡單了？