Java thinks a method is static?

Question

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();
 }
 /* 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();

• Karthik Ramachandran: could you post the error
• asgs: and also what ColorPanel looks like?

Answer 1

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()

• Aspiring Antelope: Inside of the ColorPanel class there's a method moveLeft that moves a dot left on the screen. Should I be calling it differently?
• Reverend Gonzo: Yeah ... ColorPanel.this gets you the enclosing instance. You could also do just moveLeft() since it'll go up to the next enclosing instance.
• Aspiring Antelope: When I try that I get... KeyListenerFrame.java:44: not an enclosing class: ColorPanel ColorPanel.this.moveLeft(); showKey is not defined within ColorPanel.
• Aspiring Antelope: That init code won't work inside showKey (<identifier> expected), nor inside actionPerformed (cannot find symbol).

Answer 2

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.

Answer 3

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.'

• Aspiring Antelope: I'm sorry, I wrote it without looking at the actual error. Any idea how to remedy this?
• user207421: @Bro mcBro: you can edit your post. If you're referring to remedying the error, see John's answer.