错误点我加了注释,谁能给个合理的解释?我查了API.没搞明白有什么区别...
package chapter6;
import javax.swing.*;
import java.awt.*;
class NotHelloWorldPanel extends JPanel{
private static final int Message_x=75;
private static final int Message_y=100;
public void paintComponent(Graphics g){
super.paintComponents(g);//本来这里不可以执行,报错.我加个s就能执行了.
g.drawString( "abc ", Message_x, Message_y);
}
}
class NotHelloWorldFrame extends JFrame{
private static final int DEFAULT_WIDTH=300;
private static final int DEFAULT_HIGHT=200;
public NotHelloWorldFrame(){
setTitle( "NotHelloWorld ");
setSize(DEFAULT_WIDTH,DEFAULT_HIGHT);
NotHelloWorldPanel panel=new NotHelloWorldPanel();
getContentPane().add(panel);
}
}
public class NotHelloWorld{
public static void main(String[] args){
NotHelloWorldFrame frame=new NotHelloWorldFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
------解决方案--------------------
加个s也是JPanel的一个方法,作用是绘制JPanel上的每个组件.
------解决方案--------------------
其实都是一样的阿，paintcomponents是container的方法，另一个是JComponent的方法，而container是component的子类。
public void paintComponents(Graphics g) {
if (isShowing()) {
GraphicsCallback.PaintAllCallback.getInstance().
runComponents(component, g, GraphicsCallback.TWO_PASSES);
}
}
protected void paintComponent(Graphics g) {
if (ui != null) {
Graphics scratchGraphics = (g == null) ? null : g.create();
try {
ui.update(scratchGraphics, this);
}
finally {
scratchGraphics.dispose();
}
}
}