Differnence between two codes of event handling

Question

hello i am learning event handling in swing but confused between two codes :-
the first code of event handling is given in book "head first java " and working fine
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Swingdemo implements ActionListener {
    JButton jbut = new JButton("Click me");
      public void go(){
        JFrame jfrm = new JFrame(" sample swing");
        JLabel jlab = new JLabel("hello Swing");
        jfrm.add(BorderLayout.NORTH,jlab);
        jfrm.add(BorderLayout.CENTER,jbut);
        jfrm.setVisible(true);
        jbut.addActionListener(this); 
        jfrm.setSize(100,100);
        jfrm.setDefaultCloseOperation(jfrm.EXIT_ON_CLOSE);
   public static void main(String[] args) {
        Swingdemo obj = new Swingdemo();
        obj.go();
public void actionPerformed(ActionEvent e)
    jbut.setText("i have been clicked");
}}THe second code which i think is fine is giving the following error :-
C:\java\iodemo\src\Swingdemo.java:26: non-static variable jbut cannot be referenced from a static context
        jfrm.add(BorderLayout.CENTER,jbut);
C:\java\iodemo\src\Swingdemo.java:28: non-static variable this cannot be referenced from a static context
        jbut.addActionListener(this); 
C:\java\iodemo\src\Swingdemo.java:28: non-static variable jbut cannot be referenced from a static context
        jbut.addActionListener(this);  the second code is as follows :-
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Swingdemo implements ActionListener {
public static void main(String[] args) {
JFrame jfrm = new JFrame(" sample swing");
JLabel jlab = new JLabel("hello Swing");
jfrm.add(BorderLayout.NORTH,jlab);
jfrm.add(BorderLayout.CENTER,jbut);
jfrm.setVisible(true);
jbut.addActionListener(this);
jfrm.setSize(100,100);
jfrm.setDefaultCloseOperation(jfrm.EXIT_ON_CLOSE);
JButton jbut = new JButton("Click me");
public void actionPerformed(ActionEvent e)
jbut.setText("i have been clicked");
Plz help me wat this error means that not static variable cannot be reffered from static context .
thanks

Answer 1

There are multiple problems in your 2nd set of code. You call this:
jfrm.add(BorderLayout.CENTER,jbut);
Before you actually create the jbut button:
JButton jbut = new JButton("Click me");
But based on the error message, you have another 'jbut' variable somewhere that's not included in the code you posted, and that's the one it's complaining about being referenced in a static context.
The problem with the static context is because all your code is in the static void main method. In that method, a Swingdemo instance doesn't exist yet, therefore any non-static variables won't exist yet either. If you move all that code into the Swingdemo constructor, and just have main create a new Swingdemo instance, that should do it.