Errors with array and JTextArea and ComboBox

[Trish Smith]

Hi all! I'm taking my first Java class (online) and have hit a huge wall trying to use swing for GUI elements. I would be extremely grateful is someone could look at my code and point me in the right direction for getting things working. This is my first post so I apologize if it is not formatted correctly.

I am attempting to set up 2 arrays -- one to store an ID number that will display in a ComboBox and one to store votes assoicated with each ID number (I would love to do this with a single array if possible) -- and two text areas to display results, plus two buttons and a combobox.

I've created private classes for the button and combobox listeners. I would like to increment the value stored in each array element when a vote is cast (vote button is pushed) and display a text chart of results when the end vote button pushed. Unfortunately, I am getting a null exception error whenever an array statement is encountered in the listeners.

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

public class VoteControls extends JPanel
{
	private final int MAX = 15;
	private final int MIN1 = 0;
	private final int MAX1 = 4;
	private final int MIN2 = 5;
	private final int MAX2 = 9;
	private final int MIN3 = 10;
	private final int MAX3 = 14;

	public JComboBox singersCombo;
	public JButton voteButton, endButton;
	public JTextArea textArea1, textArea2;
	public int singer = 0;
	public String[] singerID;
	public int[] singers;
	public Histogram chart;
	public String test;

	//constructor
	public VoteControls()
	{

		//create list of nums for singerID array
		String[] singerID = new String[MAX];
		int [] singers = new int[MAX];

		for (int i = 0; i < MAX; i++){
			singerID[i] = Integer.toString(i);
			singers[i] = 0;
			System.out.println ("singers[" + i + "]: " + singers[i]); //display init check
		}



	//create Histogram object
	chart = new Histogram(MIN1, MIN2, MIN3, MAX1, MAX2, MAX3);

	//create combobox for singer IDs
	singersCombo = new JComboBox (singerID);
	singersCombo.setBackground(Color.white);

	//set up butons for voting
	voteButton = new JButton("Cast Vote");
	voteButton.setBackground(Color.white);
	endButton = new JButton("End Voting");
	endButton.setBackground(Color.white);

	//set up text areas
	textArea1 = new JTextArea(5,40);
	JScrollPane scrollPane = new JScrollPane(textArea1);
	textArea1.setEditable(false);
	textArea1.setBackground(Color.white);

	textArea2 = new JTextArea(5,40);
	JScrollPane scrollPane2 = new JScrollPane(textArea1);
	textArea2.setEditable(false);
	textArea2.setBackground(Color.white);


	//set up panel
	setPreferredSize(new Dimension(600,200));
	setBackground(Color.cyan);
	add(singersCombo);
	add(voteButton);
	add(endButton);
	add(textArea1);
	add(textArea2);

	//set up listeners
	singersCombo.addActionListener(new ComboListener());
	voteButton.addActionListener(new ButtonListener());
	endButton.addActionListener(new ButtonListener());

}


//******************
//action listener for combo box

private class ComboListener implements ActionListener
{
	public void actionPerformed(ActionEvent event)
	{
		singer = (Integer) singersCombo.getSelectedIndex();

		textArea1.append("singer: " + Integer.toString(singer)); // just a test statement

	}
}

//**********************
//action listener for buttons

private class ButtonListener implements ActionListener
{
	public void actionPerformed(ActionEvent event)
	{
		if (event.getSource() == voteButton) {
				if ((singer >= 0) && (singer <=4)) {
					chart.addToRange1();
					//singers[1] = 1;
					test = Integer.toString(chart.get_countInRange1());
					textArea1.append(chart.toString());
					textArea1.append("\ncount: " + test);
					System.out.print (singers[1]);

			}
		}
		else if (event.getSource() == endButton){

				textArea2.append("\nVoting has ended.\n");
				for (int i = 0; i < MAX; i++){
					test = Integer.toString(singers[i]);
					//textArea2.append(test + "\n");
					//textArea.append("blah\n");
				}
			}
		}
	}
}

[Michael Dunn]

> I would love to do this with a single array if possible

create a separate class Vote (if that's what you want to call it)
it will have 2 fields
String id;
int voteCount = 0;
override toString() to return the id

create them giving each an id, add them to your array,
or add them to the comboBox (the id will show)

[Randall Twede]

not sure, but this looks wrong. you declare the arrays at the top
public String[] singerID;
then in your constructor you say this
String[] singerID = new String[MAX];
it should be just
singerID = new String[MAX];

[Trish Smith]

Michael Dunn wrote:> I would love to do this with a single array if possible

create a separate class Vote (if that's what you want to call it)
it will have 2 fields
String id;
int voteCount = 0;
override toString() to return the id

create them giving each an id, add them to your array,
or add them to the comboBox (the id will show)

I started out with a separate class for vote, but then couldn't figure out how to increment a value. Feeling VERY STUPID at this point. I have worked with arrays quite a bit, but not in Java and not with classes. I don't quite have my head wrapped around making objects yet. Here is the code for the Vote class:

//Vote.java
// This represents a vote object

public class Vote
{
	//instance data
	private int voteCount;
	String singerID;

	//constructor
	public Vote(String id, int vote)
	{
		voteCount = vote;
		singerID = id;
	}

	//returns a string representation of the vote object
	public String toString()
	{
		return Integer.toString(voteCount);
	}
}

I even started making a class for the vote array, but think that is going down the wrong path and making things too complicated.

When the vote button is clicked I want to increment a count for an array element, such as: array[i] = vote++. I tried passing the array as a parameter to the button listener (grasping at straws) but that didn't work. I don't understand how to link the events in the private listener to a value at a specific array element...

[Trish Smith]

Randall Twede wrote:not sure, but this looks wrong. you declare the arrays at the top
public String[] singerID;
then in your constructor you say this
String[] singerID = new String[MAX];
it should be just
singerID = new String[MAX];

Duh. I'm so flustered at this point. Here is the correction:

//VoteControls.java
//GUI Panel

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

public class VoteControls extends JPanel
{
	private final int MIN1 = 0;
	private final int MAX1 = 4;
	private final int MIN2 = 5;
	private final int MAX2 = 9;
	private final int MIN3 = 10;
	private final int MAX3 = 14;
	private final int newVote = 1;
	private final int MAX = 15;

	private JComboBox singersCombo;
	private JButton voteButton, endButton;
	private JTextArea textArea1, textArea2;
	private String[] singerID;
	private Histogram chart;
	private int[] votes;
	private String test;
	private int curSinger;


	//constructor
	public VoteControls()
	{

		//create list of nums for singerID array
		singerID = new String[MAX];
		votes = new int[MAX];

		for (int i = 0; i < MAX; i++){
			singerID[i] = Integer.toString(i);
			votes[i] = 0;
			System.out.println ("singerID[" + i + "]: " + singerID[i] + "\t" + "votes: " + votes[i]); //display init check
		}



	//create Histogram object
	chart = new Histogram(MIN1, MIN2, MIN3, MAX1, MAX2, MAX3);

	//create combobox for singer IDs
	singersCombo = new JComboBox (singerID);
	singersCombo.setBackground(Color.white);

	//set up butons for voting
	voteButton = new JButton("Cast Vote");
	voteButton.setBackground(Color.white);
	endButton = new JButton("End Voting");
	endButton.setBackground(Color.white);

	//set up text areas
	textArea1 = new JTextArea(5,40);
	JScrollPane scrollPane = new JScrollPane(textArea1);
	textArea1.setEditable(false);
	textArea1.setBackground(Color.white);

	textArea2 = new JTextArea(5,40);
	JScrollPane scrollPane2 = new JScrollPane(textArea1);
	textArea2.setEditable(false);
	textArea2.setBackground(Color.white);


	//set up panel
	setPreferredSize(new Dimension(600,200));
	setBackground(Color.cyan);
	add(singersCombo);
	add(voteButton);
	add(endButton);
	add(textArea1);
	add(textArea2);

	//set up listeners
	singersCombo.addActionListener(new ComboListener());
	voteButton.addActionListener(new ButtonListener());
	endButton.addActionListener(new ButtonListener());

}

//******************
//action listener for combo box

private class ComboListener implements ActionListener
{
	public void actionPerformed(ActionEvent event)
	{
		curSinger = (Integer) singersCombo.getSelectedIndex();

		textArea1.append("curSinger: " + Integer.toString(curSinger)); // just a test statement

	}
}

//**********************
//action listener for buttons

private class ButtonListener implements ActionListener
{
	public void actionPerformed(ActionEvent event)
	{
		if (event.getSource() == voteButton) {
				if ((curSinger >= 0) && (curSinger <=4)) {
					chart.addToRange1();
					//votes.addToVoteCount();



					test = Integer.toString(chart.get_countInRange1());
					textArea1.append(chart.toString());
					textArea1.append("\ncount: " + test);
					textArea1.append("\ncurSinger: " + curSinger);
					//System.out.print (singers[1]);

			}
		}
		else if (event.getSource() == endButton){

				textArea2.append("\nVoting has ended.\n");
				for (int i = 0; i < MAX; i++){
					//test = Integer.toString(singers[i]);
					//textArea2.append(test + "\n");
					//textArea.append("blah\n");
				}
			}
		}
	}
}

[Trish Smith]

I appreciate the help! I have two different Java books open and am hoping an "aha" moment will happen. This was my stab at a VoteArray class:

 //VoteArray.java

public class VoteArray
{
	//instance data
	private final int MAX = 15;
	private Vote[] singerVotes;
	private int singer;
	private int vote;

	//constructor
	public VoteArray()
	{
		singerVotes = new Vote[MAX];
		singer = 0;
		vote = 0;
	}

	//mutator: adds a vote to the array
	public void addVote(int singer)
	{
		singerVotes[singer] = new Vote();
	}

	//accessor: gets voteCount
	public int get_voteCount()
	{
		return vote;
	}

	//method: increment voteCount
	public void addToVoteCount()
	{
		singerVotes[singer] = vote++;
	}

	//returns a string display
	public String toString()
	{
		return Integer.toString(singer);//placeholder	}
}

[Michael Dunn]

not really sure what you're trying to achieve with arrays,
but here's a simple version of one or two things you're trying

run it, select a candidateID from the comboBox, click the 'Vote' button.
repeat numerous times

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class Testing
{
  JComboBox candidates = new JComboBox();
  JTextArea ta = new JTextArea(15,10);
  JButton btn = new JButton("Vote");
  public void buildGUI()
  {
    for(int x = 10; x < 100; x += 10) candidates.addItem(new Candidate("10"+x));
    JPanel p = new JPanel();
    p.add(candidates);
    p.add(btn);
    JFrame f = new JFrame();
    f.getContentPane().add(p,BorderLayout.NORTH);
    f.getContentPane().add(new JScrollPane(ta),BorderLayout.CENTER);
    f.pack();
    f.setLocationRelativeTo(null);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
    btn.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        ((Candidate)candidates.getSelectedItem()).voteCount++;
        ta.setText("Vote Statistics:\n\n");
        for(int x = 0, y = candidates.getItemCount(); x < y; x++)
        {
          Candidate candidate = (Candidate)candidates.getItemAt(x);
          ta.append(candidate.candidateID+": "+candidate.voteCount+"\n");
        }
      }
    });
  }
  public static void main(String[] args)
  {
    SwingUtilities.invokeLater(new Runnable(){
      public void run(){
        new Testing().buildGUI();
      }
    });
  }
}
class Candidate
{
  String candidateID;
  int voteCount = 0;
  public Candidate(String id)
  {
    candidateID = id;
  }
  @Override
  public String toString()
  {
    return candidateID;
  }
}

[Trish Smith]

Thanks Michael. This is an assignment which is why we have to do it with arrays. There are other parameters and restrictions as well, so we can't use features like SwingUtilities, each class has to be in a separate file, etc...

[Trish Smith]

I finally got it to work! Thanks for the help.

[Darryl Burke]

Trish Smith wrote:we can't use features like SwingUtilities

Don't be silly. How else are you going to launch the GUI on the EDT?

Are you allowed to use EventQueue?

[Trish Smith]

Darryl Burke wrote:

Trish Smith wrote:we can't use features like SwingUtilities

Don't be silly. How else are you going to launch the GUI on the EDT?

Are you allowed to use EventQueue?

No. This is an intro level course and the instructor is very clear about what we can and cannot use. Each assignment is focused on a particular concept and may not necessarily lead to a "real world" programming solution.

To get things finally working, I modified the Vote class (thanks for the feedback received in this forum):

//Vote.java
// This represents a vote object

public class Vote
{
	//instance data
	private int voteCount;
	private int singerID;
	private String display;

	//constructor
	public Vote(int id, int vote)
	{
		voteCount = vote;
		singerID = id;
	}

	//mutator: increment votes for a singer
	public void addVote()
	{
		voteCount++;
	}

	//returns a string representation of the vote object
	public String toString()
	{
		display = singerID + "\t" + voteCount + "\n";
		return display;
	}
}

Modified the toString method in the Histogram class (a required element):

//method: build histogram
	private String getStars(int min, int max, int count)
	{
		String temp, minRange, maxRange;
		minRange = Integer.toString(min);
		temp = minRange + " - " + Integer.toString(max) + ": ";
		stars1="";
		for (int i = 0; i < count; i++)
			stars1 = stars1 + "*";

		temp += stars1 + line;

		return temp;
	}


	//returns a string display
	public String toString()
	{
		// build histogram display
		histogram = line + "HISTOGRAM" + line;

		String temp1 = "";
		temp1 = getStars(minRange1, maxRange1, countInRange1);
		String temp2 = "";
		temp2 = getStars(minRange2, maxRange2, countInRange2);
		String temp3 = "";
		temp3 = getStars(minRange3, maxRange3, countInRange3);

		histogram += temp1 + temp2 + temp3;
		return histogram;
	}

Then created the array objects (still using two because I ran out of time to get the single array solution working) in the VoteControls class:

//create array objects
		singerID = new String[MAX];
		votes = new Vote[MAX];

		for (int i = 0; i < MAX; i++){
			singerID[i] = Integer.toString(i);
			votes[i] = new Vote(i, 0);

Then modified the listeners:

//******************
//action listener for combo box

private class ComboListener implements ActionListener
{
	public void actionPerformed(ActionEvent event)
	{
		curSinger = (Integer) singersCombo.getSelectedIndex();

		//textArea1.append("curSinger: " + Integer.toString(curSinger)); // just a test statement

	}
}

//**********************
//action listener for buttons

private class ButtonListener implements ActionListener
{
	public void actionPerformed(ActionEvent event)
	{
		String stars;
		int temp;
		if (event.getSource() == voteButton) {

				// add a vote to the current singer array element
				votes[curSinger].addVote();

				if ((curSinger >= chart.get_minRange1()) && (curSinger <= chart.get_maxRange1()))
					chart.addToRange1();

				else if ((curSinger >= chart.get_minRange2()) && (curSinger <= chart.get_maxRange2()))
					chart.addToRange2();

				else if ((curSinger >= chart.get_minRange3()) && (curSinger <= chart.get_maxRange3()))
					chart.addToRange3();

				//clear text area
				textArea1.setText("");
				textArea1.append(chart.toString());

			}
		else if (event.getSource() == endButton){

				textArea2.append("\nContestant" + "\t" + "Votes\n");
				for (int i = 0; i < MAX; i++){
					textArea2.append (votes[i].toString());

Now that it works I wish I had time to go back and clean it up. It's not an elegant solution and there are stray bits of code that could be removed, but at least it does work and it was submitted by the deadline, with 30 minutes to spare. ;-)

[Randall Twede]

i noticed this also when i went to college the last time. they made me use arrays and vectors when we had ArrayList and others