super.paintComponent问题（g） [英] problem with super.paintComponent(g)

问题描述

这是代码片段：

  protected void paintComponent（final Graphics g）{
 
 Runnable r = new Runnable（）{
 
 @Override 
 
 public void run（）{
 while（true）{
 super.paintComponent（g） ; //< -----错误行
 g.setColor（Color.red）; 
 g.drawOval（x，y，width，height）; 
 g.fillOval（x，y，width，height）; 
 x ++; 
 y ++; 
 width ++; 
 height ++; 
 if（width == 20）
 break; 
尝试{
 Thread.sleep（100）; 
} catch（Exception exc）{
 System.out.println（exc）; 
} 
} 
} 
}; 
主题moveIt =新主题（r）; 
 moveIt.start（）; 
} 
  

编译完整代码时产生以下错误：

  d：\UnderTest> javac mainClass.java 
 mainClass.java:18：找不到符号
 super.paintComponent （G）; 
 
 symbol：方法paintComponent（Graphics）
 location：class Object 
 1错误
  

为什么我得到这个错误？

如果这是我的完整代码：

  import java.awt。*; 
 import javax.swing。*; 
 import java.lang.Thread; 
 
类moveObjects扩展了JPanel {
 int x = 2，y = 2，width = 10，height = 10; 
 
 @Override 
 
 protected void paintComponent（final Graphics g）{
 
 Runnable r = new Runnable（）{
 
 @Override 
 
 public void run（）{
 while（true）{
 super.paintComponent（g）; 
 g.setColor（Color.red）; 
 g.drawOval（x，y，width，height）; 
 g.fillOval（x，y，width，height）; 
 x ++; 
 y ++; 
 width ++; 
 height ++; 
 if（width == 20）
 break; 
尝试{
 Thread.sleep（100）; 
} catch（Exception exc）{
 System.out.println（exc）; 
} 
} 
} 
}; 
主题moveIt =新主题（r）; 
 moveIt.start（）; 
 
 
 
 class mainClass {
 
 mainClass（）{
 buildGUI（）; 
} 
 
 public void buildGUI（）{
 JFrame fr = new JFrame（Moving Objects）; 
 movingObjects mO = new moveObjects（）; 
 fr.add（mO）; 
 fr.setVisible（true）; 
 fr.setSize（400,400）; 
 fr.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）; 
 
 
 public static void main（String args []）{
 new mainClass（）; 
 
 
 
 $ div $解析方案

你应该使用Qualified Super。

  moveObjects.super.paintComponent（g）; 
  

因为当您使用这个或 super 内部类（在这种情况下： Runnable ），您将获得内部类。如果您想使用内部类的外部类，请使用合格的这个或合格的超级。

  YourOuterClassName.this 
 YourOuterClassName.super 
  

Qualified Super是我无法在JLS中找到的术语，我自己发明的。 p>


This is the snippet :

protected void paintComponent(final Graphics g) {

 Runnable r=new Runnable() {

 @Override

  public void run() {
   while(true) {
     super.paintComponent(g);  // <----- line of error
     g.setColor(Color.red);
     g.drawOval(x,y,width,height);
     g.fillOval(x,y,width,height);
     x++;
     y++;
     width++;
     height++;
       if(width==20)
          break;
     try {
        Thread.sleep(100);
     } catch(Exception exc) {
         System.out.println(exc);
       }
   }
  }
};
 Thread moveIt=new Thread(r);
 moveIt.start();
}

The following error is produced when i compile the complete code :

d:\UnderTest>javac mainClass.java
mainClass.java:18: cannot find symbol
     super.paintComponent(g);
          ^
symbol:   method paintComponent(Graphics)
location: class Object
1 error

Why do i get this error?

In case this is my complete code :

import java.awt.*;
import javax.swing.*;
import java.lang.Thread;

class movingObjects extends JPanel {
int x=2,y=2,width=10,height=10;

@Override

protected void paintComponent(final Graphics g) {

Runnable r=new Runnable() {

 @Override

  public void run() {
   while(true) {
     super.paintComponent(g);
     g.setColor(Color.red);
     g.drawOval(x,y,width,height);
     g.fillOval(x,y,width,height);
     x++;
     y++;
     width++;
     height++;
       if(width==20)
          break;
     try {
        Thread.sleep(100);
     } catch(Exception exc) {
         System.out.println(exc);
       }
   }
  }
 };
   Thread moveIt=new Thread(r);
    moveIt.start();
    }
   }

class mainClass {

 mainClass() {
 buildGUI();
}

 public void buildGUI() {
 JFrame fr=new JFrame("Moving Objects");
 movingObjects mO=new movingObjects();
 fr.add(mO);
 fr.setVisible(true);
 fr.setSize(400,400); 
 fr.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

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

解决方案

You should use a Qualified Super.

movingObjects.super.paintComponent(g);

Because, when you use this or super inside an inner class (in this case: Runnable), you will get the innerclass. If you want to use the outer class from the inner class, use a Qualified This or a Qualified Super.

YourOuterClassName.this
YourOuterClassName.super

Qualified Super is a term I can't find in the JLS, I invented it by myself.

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