[英]Background color won't change in panel
下面的代码生成一个带按钮的窗口,但是当我运行i并按下按钮时会弹出一条错误消息。 根据Spring工具提示:
Cannot make a static reference to the non-static method setBackground(Color) from the type JComponent
据我所知,这个程序实际上是从我的Java教科书行输入的。 这是一本较旧的书,因此可能存在不兼容性,但似乎不太可能。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ButtonTest
{
public static void main(String[] args)
{
final ButtonFrame frame = new ButtonFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
}
class ButtonFrame extends JFrame
{
public ButtonFrame()
{
setTitle("Button Test");
setSize(Default_width, Default_height);
//panel
ButtonPanel panel = new ButtonPanel();
Container contentPane=getContentPane();
contentPane.add(panel);
}
public static final int Default_width = 300;
public static final int Default_height = 200;
}
class ButtonPanel extends JPanel
{
public ButtonPanel()
{
JButton yellowButton = new JButton("Yellow");
JButton blueButton = new JButton("Blue");
JButton redButton = new JButton("Red");
add(yellowButton);
add(blueButton);
add(redButton);
ColorAction yellowAction= new ColorAction(Color.YELLOW);
ColorAction redAction = new ColorAction(Color.RED);
ColorAction blueAction = new ColorAction(Color.BLUE);
yellowButton.addActionListener(yellowAction);
blueButton.addActionListener(blueAction);
redButton.addActionListener(redAction);
}
}
class ColorAction implements ActionListener
{
public ColorAction(Color c)
{
backgroundColor=c;
}
public void actionPerformed(ActionEvent event)
{
ButtonPanel.setBackground(backgroundColor);
}
private Color backgroundColor;
}
一种方法是将ColorAction
嵌套在ButtonPanel
作为内部类 ,其中它具有对封闭面板的隐式访问。
附录:如通过@Andrew汤普森和@nachokk评论指出,隐含的可及的是由合格的明确this
使用封闭类的名称。 见JLS§15.8.4。 合格 this
了解详情。 在此示例中,这两个调用是等效的:
setBackground(backgroundColor);
ButtonPanel.this.setBackground(backgroundColor);
作为一个更广泛的选择,考虑封装目标板和颜色的Action
,所概述这里 。
class ButtonPanel extends JPanel {
public ButtonPanel() {
JButton yellowButton = new JButton("Yellow");
JButton blueButton = new JButton("Blue");
JButton redButton = new JButton("Red");
add(yellowButton);
add(blueButton);
add(redButton);
ColorAction yellowAction = new ColorAction(Color.YELLOW);
ColorAction redAction = new ColorAction(Color.RED);
ColorAction blueAction = new ColorAction(Color.BLUE);
yellowButton.addActionListener(yellowAction);
blueButton.addActionListener(blueAction);
redButton.addActionListener(redAction);
}
private class ColorAction implements ActionListener {
public ColorAction(Color c) {
backgroundColor = c;
}
@Override
public void actionPerformed(ActionEvent event) {
setBackground(backgroundColor);
}
private Color backgroundColor;
}
}
ButtonPanel.setBackground()不是静态方法,因此您无法将其称为一个静态方法。 您需要ButtonPanel的具体实例来设置背景。
ButtonPanel bp = new ButtonPanel();
bp.setBackground(backgroundColor);
外观和感觉的变化也有帮助:
//UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
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