NullPointerException in Java JComboBox

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In trying to run my code i get NullPointerException error.I think the error is due to comboBox4 getselectedItem(),if i run the code using two comboxes it works fine.Any suggestion would be helpful.

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

 public class Test extends JPanel 
{
JTextField field11,field12,field13;
JComboBox comboBox2,comboBox3,comboBox4;

public Test() {

JPanel buttonPanel = new JPanel();
add(buttonPanel);
buttonPanel.setLayout(new GridLayout(0, 3, 5, 5));

field11 = new JTextField(10);
buttonPanel.add(field11);

field12 = new JTextField(10);
buttonPanel.add(field12);

field13 = new JTextField(10);
buttonPanel.add(field13);

comboBox2 = new JComboBox();
comboBox2.addItem("1");
comboBox2.addItem("2");
comboBox2.addItem("3");
buttonPanel.add(comboBox2);

comboBox2.addItemListener(new ItemListener() {

 @Override
         public void itemStateChanged(ItemEvent e) {
    if(e.getStateChange()  == ItemEvent.SELECTED) {
    change();
     }
      }
     });

   comboBox3 = new JComboBox();
   comboBox3.setEditable(true);
   buttonPanel.add(comboBox3);
   comboBox3.addItemListener(new ItemListener() {

   @Override
         public void itemStateChanged(ItemEvent e) {
    if(e.getStateChange()  == ItemEvent.SELECTED) {
    change();
    }
      }
    });

comboBox4 = new JComboBox();
comboBox4.setEditable(true);
buttonPanel.add(comboBox4);
comboBox4.addItemListener(new ItemListener() {

 @Override
         public void itemStateChanged(ItemEvent e) {
    if(e.getStateChange()  == ItemEvent.SELECTED) {
    change();
    }
      }
    });


JComboBox[] comboBoxs = new JComboBox[3];
comboBoxs[0] = comboBox2;
    comboBoxs[1] = comboBox3;
comboBoxs[2] = comboBox4;


ArrayList<String> list = new ArrayList<String>();

final StringBuilder temp = new StringBuilder();

try{
    InputStream ips=new FileInputStream("test2.txt");
        InputStreamReader ipsr=new InputStreamReader(ips);
        BufferedReader br=new BufferedReader(ipsr);

            String line;
    //boolean found = false;

        while ((line=br.readLine())!=null) {
        String[] s = line.split(" ");
        list.add(s[0]);
        list.add(s[1]);
    list.add(s[2]);
    }
    }       
    catch (Exception e){
        e.printStackTrace();
    }

for(int i = 0; i < comboBoxs.length; i++) {
    comboBoxs[i].setSelectedItem(list.get(i));
  }
 }

public void change() {
    Object text = comboBox2.getSelectedItem();
    if(text.toString().equals("1")) {
    field11.setText("10");
    String cb3a = ((String)comboBox3.getSelectedItem());
    double cb3b = Double.valueOf(cb3a);
    String cb3aa = field11.getText();
    double cb3bb = Double.parseDouble(cb3aa);
    double cb3c = (cb3b*cb3bb);
    String cb3d = String.valueOf(cb3c);
    field12.setText(cb3d);

    String cb4a = ((String)comboBox4.getSelectedItem());
    double cb4b = Double.valueOf(cb4a);
    double cb4c = (cb4b*cb3bb);
    String cb4d = String.valueOf(cb4c);
    field13.setText(cb4d);
    }
    else if(text.toString().equals("2")) { 
            field11.setText("20");
    String cb33a = ((String)comboBox3.getSelectedItem());
    double cb33b = Double.valueOf(cb33a);
    String cb33aa = field11.getText();
    double cb33bb = Double.parseDouble(cb33aa);
    double cb33c = (cb33b*cb33bb);
    String cb33d = String.valueOf(cb33c);
    field12.setText(cb33d);
    }
    else if(text.toString().equals("3")) {
    field11.setText("30"); 
    String cb333a = ((String)comboBox3.getSelectedItem());
    double cb333b = Double.valueOf(cb333a);
    String cb333aa = field11.getText();
    double cb333bb = Double.parseDouble(cb333aa);
    double cb333c = (cb333b*cb333bb);
    String cb333d = String.valueOf(cb333c);
    field12.setText(cb333d);

    }
}

public static void main(String[] args) {
Test app = new Test();
JFrame m = new JFrame("D");
m.getContentPane().add(app);
m.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
m.pack();
m.setVisible(true);
 }
}

test2.txt: 1 2 4

asked 51 secs ago

user

3

NullPointerException in Java JComboBox