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Resolving errors with comboboxes instance variables

Previously, I had double declared combobox object variables. I then declared them as private variables cb1,cb2 and removed the double declaration. This worked well with the sample program. However, when I do this to my class this created a few errors of the same vaiables that I cannot resolve including the private declaration.

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Font;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.ListCellRenderer;

public class HelloWorld {

	private JCombobox cb1, cb2;
	
	public static void main(String[] args) {
		// START ComboBox Image Setup
	       ImageIcon[] images;
			String[] comboStrings = {"create new po", "browse and select"};
	        images = new ImageIcon[comboStrings.length];	//array size
	        Integer[] intArray = new Integer[comboStrings.length];
	        ComboBoxRenderer renderer= new ComboBoxRenderer();
	        for (int i = 0; i < comboStrings.length; i++) {
	            intArray[i] = new Integer(i);
	            images[i] = renderer.createImageIcon("images/" + comboStrings[i] + ".jpg");  // creates image; send path

	            Image img = images[i].getImage();	// scales image size   
	            Image newimg = img.getScaledInstance(30,30, java.awt.Image.SCALE_SMOOTH);
	            images[i] = new ImageIcon(newimg);
	                        
	            if (images[i] != null) {  // sets image description
	                images[i].setDescription(comboStrings[i]);
	            }
	        }
	     // END ComboBox Image Setup

	        cb1 = new JComboBox(images);
	        cb1.setRenderer(renderer);  // displays image description
	        cb1.setMaximumRowCount(2);

	        String[] xxx = {"1111111111", "222"};
	        cb2 = new JComboBox(xxx);

	        ClickListener cl = new ClickListener();
	        cb1.addActionListener(cl);
	        cb2.addActionListener(cl);

	        JFrame f = new JFrame("teerer");
	        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	        JPanel p = new JPanel();

	        p.add(cb1);
	        p.add(cb2);
	        f.add(p);
	        f.setSize(300, 300);
	        f.setVisible(true);
	}
	  private class ClickListener implements ActionListener {

		    public void actionPerformed(ActionEvent e) {
//				System.out.println(e.getSource().equals(cb1));
				if (e.getSource().equals(cb1)) {
			          System.out.println("You've seleccted - cb1");
				}
			  	if (e.getSource().equals(cb2)) {
			          System.out.println("You've seleccted - cb2");
			  	}
			  	if(cb1.getSelectedItem().equals("1111")) {
			  		System.out.println("or right "+cb1.getSelectedItem());
			  		
			  	}
		    }
		  }
}

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for_yan

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for_yan

What are the errors?

Or post ComboBoxRenderer - otherwise I cannot compile it

for_yan

You should make them static in your case - in general that is not good way to do thinsg
private static JComboBox cb1, cb2;

SOLUTION

for_yan

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for_yan

In general it is definitely bad practice to do all that stuff in method main()

for_yan

Waht you should do - you should make a class which extends JFrame, then instatiate, bulild and place all your elements in the
constructor of this class.

Then usually the only styatement you will have in main() would be

new MyClassExtendingJFrame();

That would be much more reasonabnle way
and woill not cause any issues with static variables in main()

for_yan

Each static varaibale is unique for the whole class

Instance variable exists within every instance - and its value in one instance may be different
than in another isntance.

static method is static because it does not ddpend on any istance - therefore it is claaed with reference
only to class as a whole not to any instance - MyClass.myStaticMethod()

as ooppose to instance method which is invoked on specific instance:

MyClass instanceOfMyClass = new MyClass();
instanceOfMyClass.myInstanceMethod();

therefore static method cannot depden on the instance variables - as it should give
teh saem result for given class and is not specific to any instance

therefore you cannot use instance varaibnles within the body of your static method.

method main() is static ----> youcannot use instance variables within the main() method

That was the reason for your compiler errors

Vanavah Edwards

ASKER

You suggest is correct. I tried them and all the errors disappear as you said but now it come up with a fatal error "java.lang.NoSuchMethodError: main
Exception in thread "main" "
I even removed the image part to make it easier but still the same problem

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Font;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.ListCellRenderer;

public class HelloWorld {

	private static JComboBox cb1, cb2;
	
	public void main(String[] args) {

			String[] aaa = {"aaa", "bbb", "ccc"};
			cb1 = new JComboBox(aaa);
//	        cb1.setRenderer(renderer);  // displays image description
//	        cb1.setMaximumRowCount(2);

	        String[] xxx = {"1111111111", "222"};
	        cb2 = new JComboBox(xxx);

	        ClickListener cl = new ClickListener();
	        cb1.addActionListener(cl);
	        cb2.addActionListener(cl);

	        JFrame f = new JFrame("teerer");
	        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	        JPanel p = new JPanel();

	        p.add(cb1);
	        p.add(cb2);
	        f.add(p);
	        f.setSize(300, 300);
	        f.setVisible(true);
	}
	  private class ClickListener implements ActionListener {

		    public void actionPerformed(ActionEvent e) {
//				System.out.println(e.getSource().equals(cb1));
				if (e.getSource().equals(cb1)) {
			          System.out.println("You've seleccted - cb1");
				}
			  	if (e.getSource().equals(cb2)) {
			          System.out.println("You've seleccted - cb2");
			  	}
			  	if(cb1.getSelectedItem().equals("1111")) {
			  		System.out.println("or right "+cb1.getSelectedItem());
			  		
			  	}
		    }
		  }
}

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SOLUTION

for_yan

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Vanavah Edwards

ASKER

I accidentally changed that but chagned it back. However, after I did that the attached line of code comes up with this error "No enclosing instance of type HelloWorld is accessible. Must qualify the allocation with an enclosing instance of type HelloWorld (e.g. x.new A() where x is an instance of HelloWorld)."

ClickListener cl = new ClickListener();

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SOLUTION

for_yan

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for_yan

so make your inner class static

Once again, as I told you all this is incorrect approach.

You shoudl craete all your elements and listemers etc in constructor of the
class which extends JFrame

Method main() should usually conatins only few lines and careate instance of your class
new FrameClassname();
Then you would not have all these problems and that would be much more logiacal

SOLUTION

for_yan

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for_yan

This is very basic template which should work for you for 90% simple applications:

Use it and you'll never have these kind of problems with static main, etc.

public class MyFrame extends JFrame implements ActionListener {

private JComboBox cb1;
private JTextField tf;

public MyFrame(...) {
super("My Frame");

tf = new JTextField(10);
cb1 = JComboBox(..);
cb1.addActionListener(this);

JLabel lbl = new JLabel("tratatat");

....

//set layouts, carete panels, populate panels, add papnels to top window, specify size of window, make it all visible
this.setVisible(true);

}  // end of constructor


public void myMtehod(...) {

// some methods 

}

public void actionPerformed (ActionEvent ae) {
if(ae.getSource().equals(cb1)){

// handle evbent

}

public static void main(String [] args){
//perhaps read some paerameters form args or from user input

new MyFrame(soe parameters here...);

}


}

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Vanavah Edwards

ASKER

I was checking it. It works perfect. I have to check and see if I receive more messages from you. Thanks for your patients and talent. I will check my messages and award you and post more problems now.

SOLUTION

for_yan

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Vanavah Edwards

ASKER

prompt, fast, understands problems well, can read java code very, very quickly, gives suggestions, gives code examples, direct users to the site with documents of solutions, patient, offers multiple solutions