Java 无法从类型组件对非静态方法setBackground(颜色)进行静态引用
我得到这个错误,不能用这段代码从类型组件静态引用非静态方法setBackground(Color)Java 无法从类型组件对非静态方法setBackground(颜色)进行静态引用,java,eclipse,Java,Eclipse,我得到这个错误,不能用这段代码从类型组件静态引用非静态方法setBackground(Color) public class ColourChoice { private static JPanel myContentPane = new JPanel(); public static void main(String args[]) { Object[] colourchoice = {"Default", "Orange"};
public class ColourChoice {
private static JPanel myContentPane = new JPanel();
public static void main(String args[]) {
Object[] colourchoice = {"Default", "Orange"};
String UserInput = (String) JOptionPane.showInputDialog(null, "Please choose a colour","ColourChoice",JOptionPane.PLAIN_MESSAGE, null,colourchoice, "Default");
if (UserInput.equals("Orange")) myContentPane.setBackground(Color.ORANGE);
JFrame window = new JFrame();
window.setVisible(true);
window.setSize(100, 100);
JPanel myContentPane = new JPanel();
window.setContentPane(myContentPane);
}
}
我有一个JFrame,里面有一个JPanel,通过框架和面板加载,用户可以从下拉菜单中选择颜色,该菜单将在实际窗口加载之前出现,但是,当我为颜色“panel.setBackground(color.Orange);”编写代码时它给了我上述的错误
==
来比较字符串,而是使用.equals(…)
方法。正如在本网站上讨论的那样,==
检查一个对象是否是一个对象,是否与另一个对象相同;它检查标识,而equals(或equalsIgnoreCase)方法检查字符串是否具有相同顺序的相同字符,这正是您感兴趣的java.AWT.Panel
上调用方法。请注意,变量名称应以小写字母开头。无论如何都要这样做,以避免混淆自己和他人编辑
关于更新的代码,您的问题如下:
// likely in some constructor or method
Object[] colourchoice = {"Default", "Orange"};
String UserInput = (String) JOptionPane.showInputDialog(null, "Please choose a colour","ColourChoice",JOptionPane.PLAIN_MESSAGE, null,colourchoice, "Default");
if (UserInput == "Orange") Panel.setBackground(Color.ORANGE);
GUIDesign window = new GUIDesign();
window.setVisible(true);
window.setSize(100, 100);
JPanel Panel = new JPanel(); // ***** here
window.setContentPane(Panel);
问题:
- 不要将变量命名为“Panel”。同样,变量名应该以小写字母开头
- 由于在方法或构造函数中声明此变量,这意味着*它仅在同一变量或构造函数中可见
- 同样该变量应在类级别声明为非静态变量
- 在得到建议后,您仍然使用
比较字符串--为什么==
编辑2
例如
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.*;
import javax.swing.*;
@SuppressWarnings("serial")
public class ColorBackground {
private static final int PREF_W = 600;
private static final int PREF_H = 450;
// my main JPanel. I declare it in the class
private JPanel mainPanel = new JPanel() {
public Dimension getPreferredSize() {
// so kleopatra doesn't down-vote me
return ColorBackground.this.getPreferredSize();
};
};
private JComboBox colorBox = new JComboBox(ColorChoices.values());
public ColorBackground() {
mainPanel.add(colorBox);
colorBox.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
ColorChoices choice = (ColorChoices) colorBox.getSelectedItem();
mainPanel.setBackground(choice.getColor()); // now I can call methods on the field
}
});
}
public JComponent getMainPanel() {
return mainPanel;
}
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private static void createAndShowGui() {
JFrame frame = new JFrame("Color Background");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new ColorBackground().getMainPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
enum ColorChoices {
DEFAULT("Default", null), ORANGE("Orange", Color.orange), BLUE("Blue",
Color.blue), HOT_PINK("Hot Pink", new Color(255, 64, 128));
public String getName() {
return name;
}
@Override
public String toString() {
return name;
}
public Color getColor() {
return color;
}
private ColorChoices(String name, Color color) {
this.name = name;
this.color = color;
}
private String name;
private Color color;
}
编辑3
关于您的最新代码更新:
- 从main方法中获取所有代码
- 创建一个真正的OOP投诉程序,其中包含构造函数、非静态字段和非静态方法
- 在学习Swing之前先学习Java
setBackground(…)
。你需要首先得到一个你想要设置背景的任何东西的参考,而我们无法帮助你获得你迄今为止分享的有限信息。如果您需要更多帮助,请向我们展示更多信息,特别是我们如何获得对保存您的GUI的JPanel的引用,该引用已添加到JFrame的contentPane中。@CherryW:关键是获得对要更改其背景颜色的JPanel的有效引用。此对象应分配给非静态类字段,以便其他方法可以获得该字段的句柄。对不起,我应该粘贴完整的代码,我以前粘贴的代码位于主类中,如果这对程序的运行方式有任何影响的话。
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.*;
import javax.swing.*;
@SuppressWarnings("serial")
public class ColorBackground {
private static final int PREF_W = 600;
private static final int PREF_H = 450;
// my main JPanel. I declare it in the class
private JPanel mainPanel = new JPanel() {
public Dimension getPreferredSize() {
// so kleopatra doesn't down-vote me
return ColorBackground.this.getPreferredSize();
};
};
private JComboBox colorBox = new JComboBox(ColorChoices.values());
public ColorBackground() {
mainPanel.add(colorBox);
colorBox.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
ColorChoices choice = (ColorChoices) colorBox.getSelectedItem();
mainPanel.setBackground(choice.getColor()); // now I can call methods on the field
}
});
}
public JComponent getMainPanel() {
return mainPanel;
}
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private static void createAndShowGui() {
JFrame frame = new JFrame("Color Background");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new ColorBackground().getMainPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
enum ColorChoices {
DEFAULT("Default", null), ORANGE("Orange", Color.orange), BLUE("Blue",
Color.blue), HOT_PINK("Hot Pink", new Color(255, 64, 128));
public String getName() {
return name;
}
@Override
public String toString() {
return name;
}
public Color getColor() {
return color;
}
private ColorChoices(String name, Color color) {
this.name = name;
this.color = color;
}
private String name;
private Color color;
}