Can't see variable outside the method

Question

suncica2222 0 Junior Poster

15 Years Ago

how can I trigger anything outside the method ???

like carry the boolean a outside

public void windowClosing(WindowEvent arg0) {
                System.out.println("Window Closing");
                a=true; // cant refer to non final variable a inside an inner class defined in a different method

I want to use "a" in while loop for instance

I cant get event out of that method down,it's frustrating

here's the whole program:

import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.JFrame;

public class WinLsnrExp extends JFrame {
    
	//private boolean a=true;
	
    public WinLsnrExp() {
        
        setTitle("Window listener Example : ");
        setSize(150, 150);
    }
    public static void main(String[] args) {
    	
    //int xI,yI;
    //double xD,yD;
    boolean a = false;	
    while (a){
    /*	for (int i=0;i<100;i++) {
        WinLsnrExp wle = new WinLsnrExp();
        wle.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        wle.setLocation((int)(Math.random()*1000),(int)(Math.random()*1000));
        wle.setVisible(true);
    }
   
    }}
    	//xD=1000*Math.random();
    	//int xI = (int)xD;  
      
*/
    	
    	System.out.println(Math.random());
        WinLsnrExp wle = new WinLsnrExp();
        wle.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        wle.setLocation((int)(Math.random()*1000),(int)(Math.random()*1000));
        wle.setVisible(true);
        wle.addWindowListener(new WindowListener() {
            public void windowClosed(WindowEvent arg0) {
                System.out.println("Window close event occur");
            }
            public void windowActivated(WindowEvent arg0) {
                System.out.println("Window Activated");
            }
            public void windowClosing(WindowEvent arg0) {
                System.out.println("Window Closing");
                a=true; // cant refer to non final variable a inside an inner class defined in a different method
            }
            public void windowDeactivated(WindowEvent arg0) {
                System.out.println("Window Deactivated");
            }
            public void windowDeiconified(WindowEvent arg0) {
                System.out.println("Window Deiconified");
            }
            public void windowIconified(WindowEvent arg0) {
                System.out.println("Window Iconified");
            }
            public void windowOpened(WindowEvent arg0) {
                System.out.println("Window Opened");
            }
        });
    }
}
}

java

3 Contributors
11 Replies
277 Views
1 Week Discussion Span
Latest Post 15 Years Ago Latest Post by suncica2222

Xhamolk_ 0 Newbie Poster

15 Years Ago

You need to declare a as a global variable/field.
To do so, you need to declare it outside all the methods, but still inside your class.
I saw you had declared it as a globar & private field, but you commented it.

I fixed your code, all i did was commenting the declaration of the local variable a in your main method, and uncomment the global declaration.

import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.JFrame;

public class WinLsnrExp extends JFrame {
    
	private boolean a=true;
	
    public WinLsnrExp() {
        
        setTitle("Window listener Example : ");
        setSize(150, 150);
    }
    public static void main(String[] args) {
    	
    //int xI,yI;
    //double xD,yD;
    /*boolean*/ a = false;	
    while (a){
    /*	for (int i=0;i<100;i++) {
        WinLsnrExp wle = new WinLsnrExp();
        wle.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        wle.setLocation((int)(Math.random()*1000),(int)(Math.random()*1000));
        wle.setVisible(true);
    }
   
    }}
    	//xD=1000*Math.random();
    	//int xI = (int)xD;  
      
*/
    	
    	System.out.println(Math.random());
        WinLsnrExp wle = new WinLsnrExp();
        wle.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        wle.setLocation((int)(Math.random()*1000),(int)(Math.random()*1000));
        wle.setVisible(true);
        wle.addWindowListener(new WindowListener() {
            public void windowClosed(WindowEvent arg0) {
                System.out.println("Window close event occur");
            }
            public void windowActivated(WindowEvent arg0) {
                System.out.println("Window Activated");
            }
            public void windowClosing(WindowEvent arg0) {
                System.out.println("Window Closing");
                a=true; // cant refer to non final variable a inside an inner class defined in a different method
            }
            public void windowDeactivated(WindowEvent arg0) {
                System.out.println("Window Deactivated");
            }
            public void windowDeiconified(WindowEvent arg0) {
                System.out.println("Window Deiconified");
            }
            public void windowIconified(WindowEvent arg0) {
                System.out.println("Window Iconified");
            }
            public void windowOpened(WindowEvent arg0) {
                System.out.println("Window Opened");
            }
        });
    }
}
}

VernonDozier 2,218 Posting Expert

15 Years Ago

You need an instance of WinLsnrExp to use the a variable. You don't have one when you are trying to use a in main. a is not a static variable. main is a static function. Google "java static method" and "java static variable" for more information on what the word "static" means.

You need to create an instance of WinLsnrExp. Stick that code in your constructor or some other non-static function. Make main short. In particular, don't use a in main.

public WinLsnrExp()
{
    // code
}

public void dostuff ()
{
    // code using a that used to be in main
}

public static void main (String args[])
{
     WinLsnrExp wle = new WinLsnrExp ();
     wle.dostuff (); // you have an instance, so you can use a.
}

Since I don't understand what you are trying to do and what a represents, I can't give much more advice.

iamthwee commented: spot on +21

Xhamolk_ 0 Newbie Poster

15 Years Ago

oops,

I didn't checked the code carefully enough.

You need to turn your private boolean a to private static.

~ Xhamolk_

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suncica2222 0 Junior Poster · Answer 1 · 2009-06-07T16:35:28+00:00

sorry,but that wont work :)

it gives me a //cannot make a static reference to the non static field a

I've commented in code lines where it pop ups

and what is this "});" anyway?

import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.JFrame;

public class WinLsnrExp extends JFrame {
    
	private boolean a=true;
	
    public WinLsnrExp() {
        
        setTitle("Window listener Example : ");
        setSize(150, 150);
    }
    public static void main(String[] args) {
    	
    //int xI,yI;
    //double xD,yD;
    /*boolean*/ a = false;	    //cannot make a static reference to the non static field a
    while (a){       //cannot make a static reference to the non static field a
    /*	for (int i=0;i<100;i++) {
        WinLsnrExp wle = new WinLsnrExp();
        wle.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        wle.setLocation((int)(Math.random()*1000),(int)(Math.random()*1000));
        wle.setVisible(true);
    }
   
    }}
    	//xD=1000*Math.random();
    	//int xI = (int)xD;  
      
*/
    	
    	System.out.println(Math.random());
        WinLsnrExp wle = new WinLsnrExp();
        wle.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        wle.setLocation((int)(Math.random()*1000),(int)(Math.random()*1000));
        wle.setVisible(true);
        wle.addWindowListener(new WindowListener() {
            public void windowClosed(WindowEvent arg0) {
                System.out.println("Window close event occur");
            }
            public void windowActivated(WindowEvent arg0) {
                System.out.println("Window Activated");
            }
            public void windowClosing(WindowEvent arg0) {
                System.out.println("Window Closing");
                a=true; //cannot make a static reference to the non static field a
            }
            public void windowDeactivated(WindowEvent arg0) {
                System.out.println("Window Deactivated");
            }
            public void windowDeiconified(WindowEvent arg0) {
                System.out.println("Window Deiconified");
            }
            public void windowIconified(WindowEvent arg0) {
                System.out.println("Window Iconified");
            }
            public void windowOpened(WindowEvent arg0) {
                System.out.println("Window Opened");
            }
        });
    }
}
}

suncica2222 0 Junior Poster · Answer 2 · 2009-06-08T03:45:00+00:00

You need an instance of WinLsnrExp to use the a variable. You don't have one when you are trying to use a in main. a is not a static variable. main is a static function. Google "java static method" and "java static variable" for more information on what the word "static" means.
You need to create an instance of WinLsnrExp. Stick that code in your constructor or some other non-static function. Make main short. In particular, don't use a in main.
public WinLsnrExp()
{
    // code
}

public void dostuff ()
{
    // code using a that used to be in main
}

public static void main (String args[])
{
     WinLsnrExp wle = new WinLsnrExp ();
     wle.dostuff (); // you have an instance, so you can use a.
}
Since I don't understand what you are trying to do and what a represents, I can't give much more advice.

this is very nice instruction!!!

I've done by it and it is much better and clearer now!!!

Way to go Vernon!!!

oops,
I didn't checked the code carefully enough.
You need to turn your private boolean a to private static.
~ Xhamolk_

It wont work either way hehe

You can try if you dont believe.

VernonDozier 2,218 Posting Expert Featured Poster · Answer 3 · 2009-06-08T05:16:48+00:00

This program compiles and runs. I don't think you'd ever want to write this program, but it compiles and runs.

public class SomeClass
{
    private static boolean a;
	
    public static void main (String args[])
    {
        a = false;
        System.out.println (Boolean.toString (a));
    }
}

suncica2222 0 Junior Poster · Answer 4 · 2009-06-08T16:19:18+00:00

this doesn't compile:

public void windowClosing(WindowEvent arg0) {
                System.out.println("Window Closing");
                a=true; //cannot make a static reference to the non static field a
            }

import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.JFrame;

public class WinLsnrExp extends JFrame {
    
	private static boolean a=false;
	
    public WinLsnrExp() {
        
        setTitle("Window listener Example : ");
        setSize(150, 150);
    }
    public static void main(String[] args) {
    	


    	
    	System.out.println(Math.random());
        WinLsnrExp wle = new WinLsnrExp();
        wle.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        wle.setLocation((int)(Math.random()*1000),(int)(Math.random()*1000));
        wle.setVisible(true);
        wle.addWindowListener(new WindowListener() {
            public void windowClosed(WindowEvent arg0) {
                System.out.println("Window close event occur");
            }
            public void windowActivated(WindowEvent arg0) {
                System.out.println("Window Activated");
            }
            public void windowClosing(WindowEvent arg0) {
                System.out.println("Window Closing");
                a=true; //cannot make a static reference to the non static field a
            }
            public void windowDeactivated(WindowEvent arg0) {
                System.out.println("Window Deactivated");
            }
            public void windowDeiconified(WindowEvent arg0) {
                System.out.println("Window Deiconified");
            }
            public void windowIconified(WindowEvent arg0) {
                System.out.println("Window Iconified");
            }
            public void windowOpened(WindowEvent arg0) {
                System.out.println("Window Opened");
            }
        });
    }
}
}

VernonDozier 2,218 Posting Expert Featured Poster · Answer 5 · 2009-06-08T19:44:05+00:00

No, it doesn't. But the reason it doesn't has nothing to do with the static variable and method. Take out the extra bracket at the end and it will compile and run. However, I still prefer the approach from post 4. I don't think a should be a static variable.

suncica2222 0 Junior Poster · Answer 6 · 2009-06-08T20:07:04+00:00

You are right!

LOL how compiler gave me this error

a=true; //cannot make a static reference to the non static

for extra }

weird

Xhamolk_ 0 Newbie Poster · Answer 7 · 2009-06-08T20:31:39+00:00

I think its due to what the compiler checks first..

Anyways, if you know the error the compiler tells you is already solver, move out and check for other type of errors.

suncica2222 0 Junior Poster · Answer 8 · 2009-06-14T17:15:48+00:00

this thread is solved!!!

thank you very much xhamolc and vernon!!!