How to dispose jframe

Question

I have a jframe object in a class and I want to be able to close the frame from my jpanel class(which obviously I attach to the frame). Anyway, I tried making a instance field in my jpanel with the jframe object has an instance field and then made a method that I would call in the jframe class with the parameter of the jframe object I made so I could make the jpanel instance field the same object as the jframe object. I then called the instance field.dispose(); hoping it would close the frame. Any ideas would be greatly appreciated!

In case that was hard to understand here is an example:

public class example extends jFrame
{
public static void main(String[]args)
{
    examplePanel ep = new examplePanel();
    example e = new example(ep);

}
/**
 * Constructor for objects of class example
 */
 public example(examplePanel ep)
 {
    //code that handles my frame settings
 }
 }

  public class examplePanel extends jPanel implements ActionListener
  {
   private example e;
   private boolean checkWin;
   public void actionPerformed(ActionEvent e)
   {
    if(this.checkWin())
   {
       setVisible(false);
       e.dispose();
       //^this line of code is supposed to dispose of the frame but it does  not
   }  
   }

   public void getExample(example e)
   {
    this.e = e;
   }

  }

Answer 1

Your code and question are hard to follow as you have an ActionListener which you add to no JButton or JMenuItem, You create a JFrame object and a JPanel, but are never observed to add the panel to the frame. You give your JPanel an "example" variable, but never assign it a reference to the visualized JFrame, you don't appear to ever set the default close operation of the JFrame, and so your JFrame as written above should be non-closable. From your code it looks like your examplePanel's e variable in the JPanel should in fact be null and so calling any method on it should throw a NullPointerException, that is unless you're assigning the correct JFrame object reference to it, but are not showing us.

Myself, I'd get the top level window from Swing itself when needed, something like:

        @Override
        public void actionPerformed(ActionEvent e) {
            // get the top-level window that is displaying this JPanel
            Window win = SwingUtilities.getWindowAncestor(this);
            if (win != null) {
                win.dispose();  // dispose of it
            }
        }

For example:

import java.awt.Dimension;
import java.awt.Window;
import java.awt.event.*;
import javax.swing.*;

public class CloseFromJPanel extends JPanel implements ActionListener {
    private static final int PREF_W = 400;
    private static final int PREF_H = 300;

    public CloseFromJPanel() {
        JButton closeButton = new JButton("Close Me");
        closeButton.addActionListener(this);

        add(closeButton);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // get the top-level window that is displaying this JPanel
        Window win = SwingUtilities.getWindowAncestor(this);
        if (win != null) {
            win.dispose();  // dispose of it
        }
    }

    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    private static void createAndShowGui() {
        JFrame frame = new JFrame("Close From JPanel");

        // GUI will exit when the JFrame is closed
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new CloseFromJPanel());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }

}

This code will work for JButtons within JFrames and JDialogs, but not JMenuItems or within JApplets (I don't think). Or if all you want to do is end the application, then you could simply call System.exit(0) from within the actionPerformed method. If you absolutely want to do this using a field of the JFrame, then you'll need to pass in a reference to the JFrame into the JPanel, likely using a constructor parameter, and possibly passing in this.

If this doesn't help, please create and post real code, not kind-of sort-of code, code that we can compile, run and actually test, an MCVE (please check out the link).

Other issues:

• Your code does not comply with Java naming standards as class names should all start with capital letters. Please Google this and study it, since if your code follows standards, others, including both us and your future self, will better be able to understand your code.
• You'll rarely want to ever extend from JFrame since you rarely need to alter it's innate behavior. Usually you'll create and use a JFrame or JDialog when and where needed.