Java JPanel-更改JPanel的背景颜色时出错
我编写了以下代码:Java JPanel-更改JPanel的背景颜色时出错,java,swing,Java,Swing,我编写了以下代码: import java.awt.Color; import java.awt.Graphics; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; import javax.swing.JFrame; import javax.swing.JPanel; public class Test extends JFrame{ public Test() {
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Test extends JFrame{
public Test() {
this.setTitle("Test");
this.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
JPanel jPanel = new JPanel() {
public void paint(Graphics g) {
g.setColor(Color.GREEN);
g.fillOval(100, 100, 100, 100);
g.setColor(Color.BLACK);
g.drawLine(0, 0, 100, 100);
}
};
jPanel.setSize(500, 500);
jPanel.setBackground(Color.RED);
this.add(jPanel);
this.setVisible(true);
this.setSize(500, 500);
}
public static void main(String[] args) {
Test test = new Test();
}
}
我想画一个圆,画一条线,然后将屏幕的背景色更改为红色,但当我运行程序时,屏幕显示如下:
代码中的错误在哪里?。首先,不要覆盖
paint
,而要覆盖paintComponent
然后,setBackground
的javadoc说:
JComponent的直接子类必须重写paintComponent以实现
这是我的财产
因此,在您的情况下,调用此方法本身不会起任何作用,除非您调用父类的paintComponent
(或者自己绘制背景,但这样做太过分了)
在任何情况下,建议调用super.paintComponent
,因为父实现可能会执行一些清理或其他有用的操作
下面是代码的修改版本,其中考虑了所有这些因素:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Test extends JFrame {
public Test() {
this.setTitle("Test");
this.addWindowListener(new WindowAdapter() {
public void windowClosing(final WindowEvent e) {
System.exit(0);
}
});
JPanel jPanel = new JPanel() {
@Override
public void paintComponent(final Graphics g) {
// call parent method
super.paintComponent(g);
// OR paint background yourself :
// g.setColor(getBackground());
// g.fillRect(0, 0, getWidth(), getHeight());
// paint other things
g.setColor(Color.GREEN);
g.fillOval(100, 100, 100, 100);
g.setColor(Color.BLACK);
g.drawLine(0, 0, 100, 100);
}
};
jPanel.setSize(500, 500);
jPanel.setBackground(Color.RED);
this.add(jPanel);
this.setVisible(true);
this.setSize(500, 500);
}
public static void main(final String[] args) {
Test test = new Test();
}
}
感谢您的帮助,您是否推荐任何书籍、网页或其他资源来学习Java GUI开发?@Lemark:Oracle的教程是一个良好的开端: