java程序繪製一個固定的多邊形

Question

我正在寫一個程序，繪製一個固定的多邊形與某些點，並告訴鼠標點是否在多邊形的內部或外部。我不知道在哪裏需要移動代碼，以便我可以修復這些錯誤。我很確定有什麼是錯誤的地方。這就是我現在所擁有的：

import javax.swing.JFrame; 
import javax.swing.JPanel; 
import java.awt.Graphics; 
import java.awt.event.MouseAdapter; 
import java.awt.event.MouseEvent; 
import java.awt.BorderLayout; 
import java.awt.Point; 
import java.awt.Polygon; 

public class Ch3PA extends JFrame { 

    Polygon polygon = new Polygon(); 
    Point point = new Point(0, 0); 
    boolean inside = false; 
    private PaintPanel paintPanel = new PaintPanel(); 

    public PaintPanel() 
    { 
     add(paintPanel); 

     static class PaintPanel extends JPanel 
     {  
      polygon.addPoint(40, 20); 
      polygon.addPoint(70, 40); 
      polygon.addPoint(60, 80); 
      polygon.addPoint(45, 45); 
      polygon.addPoint(20, 60); 

      @addMouseMotionListener(new MouseAdapter() 
      { 
       public void mouseMoved(MouseEvent e) 
       { 
        point.x = e.getX(); 
        point.y = e.getY(); 
        if (polygon.contains(e.getX(), e.getY())) 
        { 
         inside = true; 
         repaint(); 
        } 
        else 
        { 
         inside = false; 
         repaint();    
        } 
       } 
      }); 
     } 
    } 

    protected void paintComponent(Graphics g){ 
     super.paintComponents(g); 
     g.drawPolygon(polygon); 
     if (inside) 
     { 
      g.drawString(inside ? "Mouse point is in the polygon" :   "Mouse point is not in the polygon", point.x, point.y); 
      repaint(); 
     }    
    } 

    public static void main(String[] args) { 
     Ch3PA frame = new Ch3PA(); 
     frame.setTitle("Ch3PA"); 
     frame.setLocationRelativeTo(null); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.setSize(200, 200); 
     frame.setVisible(true);   
    } 
} 

Answer 1

這...

public class Ch3PA extends JFrame { 

    //... 
    public PaintPanel() 

是沒有意義的。您已經定義了一個名爲Ch3PA類，而是定義了一個名爲PaintPanel構造它

然後定義構造函數中的類....

static class PaintPanel extends JPanel 
{ 

    polygon.addPoint(40, 20); 
    polygon.addPoint(70, 40); 
    polygon.addPoint(60, 80); 
    polygon.addPoint(45, 45); 
    polygon.addPoint(20, 60); 



@addMouseMotionListener(new MouseAdapter() 
{ 
    public void mouseMoved(MouseEvent e) 
    { 
     point.x = e.getX(); 
     point.y = e.getY(); 

     if (polygon.contains(e.getX(), e.getY())) 
     { 
      inside = true; 
      repaint(); 
     } 
      else 
      { 
       inside = false; 
       repaint(); 

     } 
    } 

}); 

即使這是合法的，在polygon.addPoint韓元」將不起作用，因爲你想一個可執行上下文之外執行代碼（方法，構造函數，static塊）

@addMouseMotionListener是非法的語法，你不應該用@

0領先

不要叫repaint();任何paint方法裏面，這會消耗你的CPU與上房重繪

你打電話super.paintComponents < - 注意s，這是不是你正在尋找的方法。你應該打電話給super.paintComponent，但我懷疑你的IDE不適合並且不知道如何解決它。還有一種情況@Override註釋是這樣的幫助，但我懷疑，因爲其他所有的問題，它真的會immeditatly幫助

開始通過定義你PaintPanel，定義它的操作和責任......

public class PaintPanel extends JPanel { 

    Polygon polygon = new Polygon(); 
    Point point = new Point(0, 0); 
    boolean inside = false; 

    public PaintPanel() { 

     polygon.addPoint(40, 20); 
     polygon.addPoint(70, 40); 
     polygon.addPoint(60, 80); 
     polygon.addPoint(45, 45); 
     polygon.addPoint(20, 60); 

     addMouseMotionListener(new MouseAdapter() { 
      public void mouseMoved(MouseEvent e) { 
       point.x = e.getX(); 
       point.y = e.getY(); 

       if (polygon.contains(e.getX(), e.getY())) { 
        inside = true; 
        repaint(); 
       } else { 
        inside = false; 
        repaint(); 

       } 
      } 

     }); 
    } 

    protected void paintComponent(Graphics g) { 

     super.paintComponent(g); 

     g.drawPolygon(polygon); 

     if (inside) { 
      g.drawString(inside ? "Mouse point is in the polygon" : "Mouse point is not in the polygon", point.x, point.y); 
     } 

    } 

} 

現在，這增加一些容器

EventQueue.invokeLater(new Runnable() { 
    @Override 
    public void run() { 
     try { 
      UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
     } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { 
      ex.printStackTrace(); 
     } 

     JFrame frame = new JFrame("Testing"); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.add(new PaintPanel()); 
     frame.pack(); 
     frame.setLocationRelativeTo(null); 
     frame.setVisible(true); 
    } 
}); 

Runnable的例子...

import java.awt.EventQueue; 
import java.awt.Graphics; 
import javax.swing.JFrame; 
import java.awt.Point; 
import java.awt.Polygon; 
import java.awt.event.MouseAdapter; 
import java.awt.event.MouseEvent; 
import javax.swing.JPanel; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class Ch3PA extends JFrame { 

    public static void main(String[] args) { 
     new Ch3PA(); 
    } 

    public Ch3PA() { 
    EventQueue.invokeLater(new Runnable() { 
     @Override 
     public void run() { 
      try { 
       UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
      } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { 
       ex.printStackTrace(); 
      } 

      JFrame frame = new JFrame("Testing"); 
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
      frame.add(new PaintPanel()); 
      frame.pack(); 
      frame.setLocationRelativeTo(null); 
      frame.setVisible(true); 
     } 
    }); 
    } 

    public class PaintPanel extends JPanel { 

     Polygon polygon = new Polygon(); 
     Point point = new Point(0, 0); 
     boolean inside = false; 

     public PaintPanel() { 

      polygon.addPoint(40, 20); 
      polygon.addPoint(70, 40); 
      polygon.addPoint(60, 80); 
      polygon.addPoint(45, 45); 
      polygon.addPoint(20, 60); 

      addMouseMotionListener(new MouseAdapter() { 
       public void mouseMoved(MouseEvent e) { 
        point.x = e.getX(); 
        point.y = e.getY(); 

        if (polygon.contains(e.getX(), e.getY())) { 
         inside = true; 
         repaint(); 
        } else { 
         inside = false; 
         repaint(); 

        } 
       } 

      }); 
     } 

     @Override 
     protected void paintComponent(Graphics g) { 

      super.paintComponent(g); 

      g.drawPolygon(polygon); 

      if (inside) { 
       g.drawString(inside ? "Mouse point is in the polygon" : "Mouse point is not in the polygon", point.x, point.y); 
      } 

     } 

    } 
}