Java小程序未在Eclipse中更新';s内置小程序查看器
我只是在学习java小程序。我用drawLine()在小程序上画了一条线,当我按下run时,它正常编译并用Eclipse的内置小程序查看器显示小程序。这是密码Java小程序未在Eclipse中更新';s内置小程序查看器,java,eclipse,applet,Java,Eclipse,Applet,我只是在学习java小程序。我用drawLine()在小程序上画了一条线,当我按下run时,它正常编译并用Eclipse的内置小程序查看器显示小程序。这是密码 import java.applet.*; import java.awt.*; public class Lab04b { public void paint(Graphics g){ g.drawLine(0, 0, 200, 200); } } 但是,当我注释掉drawLine()并重新编译并运行它时,它
import java.applet.*;
import java.awt.*;
public class Lab04b {
public void paint(Graphics g){
g.drawLine(0, 0, 200, 200);
}
}
但是,当我注释掉drawLine()并重新编译并运行它时,它会显示小程序,上面有一条线,就好像代码更改时它没有更新一样。以下是注释掉的版本:
import java.applet.*;
import java.awt.*;
public class Lab04b {
public void paint(Graphics g){
//g.drawLine(0, 0, 200, 200);
}
}
我已经尝试重新打开Eclipse,但它仍然显示小程序,上面有一行,就像它第一次运行时一样。请告诉我如何让Eclipse在内置小程序查看器中更新小程序。您的Lab04b类不是小程序:
import java.applet.*;
import java.awt.*;
public class Lab04b {
public void paint(Graphics g){
g.drawLine(0, 0, 200, 200);
}
}
因为applet类必须扩展applet或JApplet,而您的类则不能。我建议:
- 让学生扩展JApplet
- 但不要直接在它里面画
- 而是在小程序中显示的JPanel的
方法中绘制paintComponent
- 请确保为小程序类提供一个
方法,它将在其中保存初始化代码init()
import java.awt.Graphics;
import java.lang.reflect.InvocationTargetException;
import javax.swing.*;
// an applet class must extend either Applet or JApplet
public class AppletTest extends JApplet {
// it should have an init() method where it holds its initialization code.
@Override
public void init() {
try {
SwingUtilities.invokeAndWait(new Runnable() {
public void run() {
add(new DrawingPanel());
}
});
} catch (InvocationTargetException | InterruptedException e) {
e.printStackTrace();
}
}
}
// avoid drawing directly within the applet itself
// but instead draw within a JPanel that is added to the applet
class DrawingPanel extends JPanel {
// this is the method to draw in
@Override
protected void paintComponent(Graphics g) {
// don't forget to call the super method to do "housekeeping" drawing
super.paintComponent(g);
g.drawLine(0, 0, 200, 200);
}
}
-
说到这里,考虑不要学习applet,因为它们现在很少使用。