help with .isSelected

[kat Vicap]

i have a problem with the Jcheckbox listener. i set the initial charge to 10. and for every checkbox selected, the charge should increment to 1. however, decrements to 1 as well when desselected. the problem with my code is that the incrementation and decrementation only works for ONE checkbox. when i the second box is selected, it wont increment the charge neither decrements when unselected. please help

  import javax.swing.*;
import java.awt.*;

public class Clinic
{
	public JFrame f;
	public JLabel l1,l3,l4;
	public JCheckBox c[];
	public JPanel p1,p2,p3,p4;
	private Events e;
	private double price = 10.0;



	public Clinic()
	{

		f= new JFrame("Lion Tigers and Bears Clinic");
		l1= new JLabel("Lion Tigers and Bears Pet Clinic \n Services");
		l3= new JLabel("Service Charge: ");
		l4= new JLabel(String.valueOf(price));

		c[0]= new JCheckBox("Office Visits");
		c[1]= new JCheckBox("Vaccination");
		c[2]= new JCheckBox("Hospitalization");
		c[3]= new JCheckBox("Heartworm Prevention");
		c[4]= new JCheckBox("Boarding");
		c[5]= new JCheckBox("Dentistry");
		c[6]= new JCheckBox("X-Rays");
		c[7]= new JCheckBox("Laboratory Work");
		c[8]= new JCheckBox("Prescriptions");
		p1= new JPanel();
		p3= new JPanel();
		p4= new JPanel();
		e= new Events(this);



	}

	public void launch()
	{
		for(int i=0;i<9;i++)
		c[i].addItemListener(e);


		f.setLayout(new FlowLayout());
		p1.add(l1);
		f.add(p1);


		p3.setLayout(new GridLayout(3,3,2,8));
		for(int i=0;i<9;i++)
		p3.add(c[i]);
		f.add(p3);

		p4.setLayout(new GridLayout(1,2));
		p4.add(l3);
		p4.add(l4);
		f.add(p4);



		f.setVisible(true);
		f.setSize(500,300);
		f.setDefaultCloseOperation(3);

	}

	public JLabel getL4()
	{
		return l4;
	}
}

  

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

public class Events implements ItemListener
{
	private Clinic c;

	public Events(Clinic c)
	{
		this.c=c;
	}

	public void itemStateChanged(ItemEvent e)
	{

		double price = 10.0;

		for(int i=0; i<9; i++)
		{
		JCheckBox c[i]= (JCheckBox).egetSource();
		if(c[i].isSelected())
		price +=1.0;


		else price -=1.0;
		c.getL4().setText(""+ price);
	}
	}
}

  

[pete stein]

Your code doesn't compile for me.

[kat Vicap]

import javax.swing.*;
import java.awt.*;

public class Clinic
{
	public JFrame f;
	public JLabel l1,l3,l4;
	public JCheckBox[] ch;
	public JPanel p1,p2,p3,p4;
	private Events e;
	private double price = 10.0;



	public Clinic()
	{

		f= new JFrame("Lion Tigers and Bears Clinic");
		l1= new JLabel("Lion Tigers and Bears Pet Clinic \n Services");
		l3= new JLabel("Service Charge: ");
		l4= new JLabel(String.valueOf(price));

		ch[0]= new JCheckBox("Office Visits");
		ch[1]= new JCheckBox("Vaccination");
		ch[2]= new JCheckBox("Hospitalization");
		ch[3]= new JCheckBox("Heartworm Prevention");
		ch[4]= new JCheckBox("Boarding");
		ch[5]= new JCheckBox("Dentistry");
		ch[6]= new JCheckBox("X-Rays");
		ch[7]= new JCheckBox("Laboratory Work");
		ch[8]= new JCheckBox("Prescriptions");
		p1= new JPanel();
		p3= new JPanel();
		p4= new JPanel();
		e= new Events(this);



	}

	public void launch()
	{
		for(int i=0;i<9;i++)
		ch[i].addItemListener(e);


		f.setLayout(new FlowLayout());
		p1.add(l1);
		f.add(p1);


		p3.setLayout(new GridLayout(3,3,2,8));
		for(int i=0;i<9;i++)
		p3.add(ch[i]);
		f.add(p3);

		p4.setLayout(new GridLayout(1,2));
		p4.add(l3);
		p4.add(l4);
		f.add(p4);



		f.setVisible(true);
		f.setSize(500,300);
		f.setDefaultCloseOperation(3);

	}

	public JLabel getL4()
	{
		return l4;
	}
}

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

public class Events implements ItemListener
{
	private Clinic c;

	public Events(Clinic c)
	{
		this.c=c;
	}

	public void itemStateChanged(ItemEvent e)
	{

		double price = 10.0;


			JCheckBox change=(JCheckBox)e.getSource();
			boolean state = change.isSelected();

			for(int i=0;i<10;i++)
			{
				if(change==c.ch[i])
				price += 1.00;

				else price -=1.00;

				c.getL4().setText(String.valueOf(price));
			}
		}
	}

  

 public class Main
{
	public static void main(String[] args)
	{
		Clinic k= new Clinic();
		k.launch();
	}
}   

but still i got a NULL POINTER EXCEPTION after i compiled.. guys please help

[pete stein]

love fox wrote:
but still i got a NULL POINTER EXCEPTION after i compiled.. guys please help

The NPE will tell you exactly which line is causing it. On that line you are trying to use an object that has not been initialized. For instance, I see that you've declared a JCheckBox array but I don't see that you've ever initialized it. Perhaps this is causing your problem.

Other suggestions:
1) Use descriptive variable names throughout. For example, instead of p2, use chkBoxPanel, instead of e, use checkBoxListener, etc...

2) use an array of String for your checkbox labels. This way you can consolidate your code quite a bit. i.e.,

      for (String checkBoxLabel : CHECKBOX_LABELS) {
         JCheckBox checkBox = new JCheckBox(checkBoxLabel);
         chkBxPanel.add(checkBox);
         checkBox.addItemListener(checkBoxListener);
      }

3) Put in clinic a public method to count the number of checkboxes clicked (easy if you have traverse the array). Have the Listener call this method.

4) Put in clinic a public method to change the charge label

[kat Vicap]

i got the thing to compile now. but the charge is so messed up.

GUI

  import javax.swing.*;
import java.awt.*;

public class Clinic
{
	public JFrame f;
	public JLabel l1,l3,l4;
	public JCheckBox[] ch;
	public JPanel p1,p2,p3,p4;
	private Events e;
	private double price = 10.0;



	public Clinic()
	{

		f= new JFrame("Lion Tigers and Bears Clinic");
		l1= new JLabel("Lion Tigers and Bears Pet Clinic \n Services");
		l3= new JLabel("Service Charge: ");
		l4= new JLabel(String.valueOf(price));

		ch= new JCheckBox[9];
		ch[0]= new JCheckBox("Office Visits");
		ch[1]= new JCheckBox("Vaccination");
		ch[2]= new JCheckBox("Hospitalization");
		ch[3]= new JCheckBox("Heartworm Prevention");
		ch[4]= new JCheckBox("Boarding");
		ch[5]= new JCheckBox("Dentistry");
		ch[6]= new JCheckBox("X-Rays");
		ch[7]= new JCheckBox("Laboratory Work");
		ch[8]= new JCheckBox("Prescriptions");
		p1= new JPanel();
		p3= new JPanel();
		p4= new JPanel();
		e= new Events(this);



	}

	public void launch()
	{
		for(int i=0;i<9;i++)
		ch[i].addItemListener(e);


		f.setLayout(new FlowLayout());
		p1.add(l1);
		f.add(p1);


		p3.setLayout(new GridLayout(3,3,2,8));
		for(int i=0;i<9;i++)
		p3.add(ch[i]);
		f.add(p3);

		p4.setLayout(new GridLayout(1,2));
		p4.add(l3);
		p4.add(l4);
		f.add(p4);



		f.setVisible(true);
		f.setSize(500,300);
		f.setDefaultCloseOperation(3);

	}

	public JLabel getL4()
	{
		return l4;
	}
}

  

EVENTS

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

public class Events implements ItemListener
{
	public Clinic c;
	double price = 10.0;

	public Events(Clinic c)
	{
		this.c=c;
	}

	public void itemStateChanged(ItemEvent e)
	{

			JCheckBox change=(JCheckBox)e.getSource();
			boolean state = change.isSelected();

			for(int i=1;i<9;i++)
			{
				if(change==c.ch[i])
				price += 1.00;

				else price -=1.00;

				c.getL4().setText(""+price);
			}
		}
	}



   

[Rob Spoor]

"love fox", you've been warned about your name before, two days ago. Apparently you have not noticed that warning; consider this a second chance to fix it.