Java thinks a method is static?
For some reason, when I try to call a non-static method from another class in an action, I get an error saying I can't call a non-static method in a static method. However, I never defined the action or its parents as static. Why do I get this error?
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class KeyListenerFrame extends JFrame implements KeyListener {
GridLayout gridLayout1 = new GridLayout();
JPanel listenerPan = new JPanel();
public KeyListenerFrame() {
try {
jbInit();
listenerPan.addKeyListener(this);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
listenerPan.getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_PAGE_UP,0,true), "showKey");
listenerPan.getActionMap().put("showKey", showKey);
listenerPan.getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, true), "showKey");
}
catch(Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
KeyListenerFrame klf = new KeyListenerFrame();
klf.setBounds(10,10,500,500);
klf.setVisible(true);
klf.focusPanel();
}
public void focusPanel() {
listenerPan.requestFocus();
}
private void jbInit() throws Exception {
this.getContentPane().add(listenerPan, null);
ColorPanel panel = new ColorPanel(Color.lightGray);
this.getContentPane().add(panel);
}
this is the part that gives me trouble
Action showKey = new AbstractAction() {
public void actionPerformed(ActionEvent e) {
ColorPanel.moveLeft();
}
};
public void keyTyped(KeyEvent e) {
System.out.println(e.toString());
}
public void keyPressed(KeyEvent e) {
System.out.println(e.toString());
}
public void keyReleased(KeyEvent e) {
System.out.println(e.toString());
}
}
ColorPanel.java
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.Component.*;
import java.awt.Container.*;
import javax.swing.JComponent.*;
public class ColorPanel extends JPanel{
public Circle circle;
private javax.swing.Timer timer;
public ColorPanel(Color backColor){
int width = 500;
int height = 500;
setBackground(backColor);
setPreferredSize(new Dimension(width, height));
circle = new Circle(width / 2, height / 2, 50, Color.red);
circle.setVelocity(5);
addMouseListener(new MoveListener());
}
public void paintComponent(Graphics g){
super.paintComponent(g);
circle.fill(g);
}
public void moveLeft(){
circle.move();
repaint();
}
/*开发者_Go百科 public class MoveListener extends MouseAdapter{
public void mousePressed(MouseEvent e){
circle.move();
repaint();
}
}
private class MoveListener implements ActionListener{
public void actionPerformed(ActionEvent e){
circle.move();
//circle.turn(1);
repaint();
}
} */
}
The error generated from the ColorPanel.moveLeft(); is: KeyListenerFrame.java:51: non-static method moveLeft() cannot be referenced from a static context ColorPanel.moveLeft();
What exactly are you trying to do here:
ColorPanel.moveLeft();
ColorPanel is a class, when it should be an instance.
What you may be intending to do is (assuming showKey is defined within ColorPanel):
ColorPanel.this.moveLeft();
Edit To Add the following:
private void jbInit() throws Exception {
this.getContentPane().add(listenerPan, null);
ColorPanel panel = new ColorPanel(Color.lightGray);
this.getContentPane().add(panel);
}
ColorPanel is created in here, but a reference isn't kept.
If you move ColorPanel panel outside of jbInit, and then initialize it as
panel = new ColorPanel(Color.lightGray);
you'll have your reference. Then instead of ColorPanel.moveLeft() call panel.moveLeft()
The problem is that you are trying to access it as you would if it were a static method. You need to create an instance of the class, then through the instance you call moveLeft().
Also create a global reference to your ColorPanel Object. This would be the instance of the ColorPanal class you call moveLeft() on.
I get an error saying I can't call a non-static method in a static method
No you don't. There is no such message and no such error. You get an error saying 'non-static method method() cannot be referenced from a static context.'
精彩评论