JComboBoxes

[Keerti]

Hi all
I am working on a UI which has 2 tabs.In the class for the first tab I declare and initialize an array of JComboBoxes.
public class tabone{
protected JComboBox[] combolist = new JComboBox[3];
public addComponents(){
for(int i=0;i<4;i++)
{
this.combolist[i] = new JComboBox();
}
//set name for JcomboBoxes
combolist[0].setName("combo1");
combolist[1].setName("combo2");
combolist[2].setName("combo3");
combolist[3].setName("combo4");
}
}

In the class for the second Tab I want to access the last two JComboBoxes.
These two claases are in the same package.
public class tabtwo extends tabone{
String name = combolist[2].getName();
This line throws up an error:Exception in thread "main" java.lang.NullPointerException

Can someone please tell why i am getting this error.
or
How should I access the JComboBoxes in the class for tabtwo?

[hardwired]

Code:

import javax.swing.JComboBox;

public class ComboTalk {
    public static void main(String[] args) {
        TabOne tabOne = new TabOne();
        TabTwo tabTwo = new TabTwo(tabOne);
        tabTwo.test(2);
    }
}

class TabOne {
    JComboBox[] combos;

    public TabOne() {
       String[] names = { "one", "two", "three" };
       combos = new JComboBox[names.length];
       for(int i = 0; i < names.length; i++) {
           combos[i] = new JComboBox();
           combos[i].setName(names[i]);
       }
    }

    public JComboBox getComboBox(int index) {
        return combos[index];
    }
}

class TabTwo {
    TabOne tabOne;

    public TabTwo(TabOne tabOne) {
        this.tabOne = tabOne;
    }

    public void test(int index) {
        JComboBox comboBox = tabOne.getComboBox(index);
        System.out.printf("combos[%d] name = %s%n",
                           index, comboBox.getName());
    }
}

[Keerti]

Hi
Thanks for the solution Hardwired.It works.
In continuation of the same UI program ..I have a few more Queries.
ComboBox[2] is present in tab2. The list for this combobox2 depends on the
value selected in combobox[1] which is present in tab1.
I have added an action listener on combobox1 .when the user selects the value, I get the list to be loaded for combobox2 in the form of a vector.
But I am not able to put this in the list for combobox2.that is i am not able to view it in the UI.The list for combobox2 remains blank

here is what I do:

listforcombo---is the vector that has to be loaded into combobox2
listforcombo = listofindevars.findependentValues(frameText,var_na me,frameText,(String) dependentVars.elementAt(i));

ComboBoxModel aModel = new DefaultComboBoxModel( listforcombo );
combolist[2].setModel(aModel);

Please help me in resolving this problem.

[hardwired]

Code:

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

public class ComboTalk {
    public static void main(String[] args) {
        TabOne tabOne = new TabOne();
        TabTwo tabTwo = new TabTwo(tabOne);
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(5,5,5,5);
        panel.add(tabOne.getComboBox(), gbc);
        panel.add(tabTwo.comboBox, gbc);
        JOptionPane.showMessageDialog(null, panel, "", -1);
    }
}

class TabOne {
    JComboBox comboBox;

    public TabOne() {
       String[] items = { "one", "two", "three" };
       comboBox = new JComboBox(items);
       
    }

    public JComboBox getComboBox() {
        return comboBox;
    }
}

class TabTwo implements ActionListener {
    TabOne tabOne;
    JComboBox comboBox;
    String[][] items = {
        { "one 1",   "one 2",   "one 3"   },
        { "two 1",   "two 2",   "two 3"   },
        { "three 1", "three 2", "three 3" }
    };

    public TabTwo(TabOne tabOne) {
        this.tabOne = tabOne;
        int index = tabOne.getComboBox().getSelectedIndex(); 
        comboBox = new JComboBox(items[index]);
        tabOne.getComboBox().addActionListener(this);
    }

    private void updateComboBox(int index) {
        comboBox.removeAllItems();
        for(int i = 0; i < items[index].length; i++) {
            comboBox.addItem(items[index][i]);
        }
    }

    public void actionPerformed(ActionEvent e) {
        JComboBox comboBox = tabOne.getComboBox();
        int index = comboBox.getSelectedIndex();
        System.out.printf("index = %d%n", index);
        updateComboBox(index);
    }
}