I keep getting NullPointerExeptions...

[Savale]

Ok.. what I'm doing is taking text from a JTextField, and putting it into a String array.

Starray[0] = text1.getText();
Starray[1] = text2.getText();

Every thing works fine until this line is executed, and I get a NullPointerException. Is there something I'm doing wrong here or what?

 

[Vepo]

Hi Savale,

Are you sure that you have initialized JTextField?
If you try to refer to object that is not initialized, you get that NullPointerException.

 

[Vepo]

...and make sure that Starray isn't null either.

 

[Savale]

JTextField was initialized properly. I have that directly after declaring the class.
here is all the code if it helps anyone...

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

public class Dmath extends javax.swing.JFrame implements ActionListener {
String num3[];

JButton mult = new JButton("*"
JButton div = new JButton("/"
JLabel num2 = new JLabel("Second Number: "
JTextField text2 = new JTextField(3);
JLabel num1 = new JLabel("First Number: "
JTextField text1 = new JTextField(3);
JTextField text3 = new JTextField(15);
JButton add = new JButton("+"
JButton subt = new JButton("-"

public Dmath(){
initComponents();
pack();
}

private void initComponents(){
addWindowListener(new java.awt.event.WindowAdapter() {
public void windowClosing(java.awt.event.WindowEvent evt) {
exitForm(evt);
}
}
);
}

private void exitForm(java.awt.event.WindowEvent evt) {
System.exit(0);
}

public static void main(String[] args){

Dmath mainWindow = new Dmath();
mainWindow.addParams(mainWindow);
mainWindow.show(false);
mainWindow.resize(150, 200);
mainWindow.show(true);
}

public void addParams(Dmath mnWin){

FlowLayout fl = new FlowLayout();
mnWin.getContentPane().setLayout(fl);

add.addActionListener(this);
subt.addActionListener(this);
mult.addActionListener(this);
div.addActionListener(this);

mnWin.getContentPane().add(num1);
mnWin.getContentPane().add(text1);
mnWin.getContentPane().add(num2);
mnWin.getContentPane().add(text2);
mnWin.getContentPane().add(add);
mnWin.getContentPane().add(subt);
mnWin.getContentPane().add(mult);
mnWin.getContentPane().add(div);
mnWin.getContentPane().add(text3);

}

public void actionPerformed(java.awt.event.ActionEvent p1) {
Object src = p1.getSource();
Doug dg;

if (src.equals(add)){
dg = new Doug();

num3[0] = text1.getText();
num3[1] = text1.getText();

try {
dg.GetSumInts(num3);
text3.setText(String.valueOf(dg.SumOf()));
}
catch (Exception e) {
System.out.println("Error: BAD MAN!!"
System.exit(0);
}

}
else if (src.equals(subt)){
dg = new subt();
}


}

}

Its just a simple calculator program, and I know its not very pretty, but any suggestions would be helpful.

thanks

 

[meadandale]

I don't see anywhere that you have initialized the array num3. You declare it as a class variable but never allocate any memory for it. You need to do:

int [] num3 = new int[2];

or however big you need it to be.

Charles

 

[LeonTang]

Erm...its a String array..not int array If you need additional help, you can email to me at zaoliang@hotmail.com I don't guaranty that I will be able to solve your problems but I will try my best

 

[pipk]

don't you need something like

starray [0] = new String(text1.getText());

or am i talking out of my arse as usual?

 

[haslo]

meadandale and LeonTang are right - the array has to be initialized first...

If you do text1.getText() you'll receive a String anyway. If you now create a

new String(text1.getText())

this does no harm - it just creates a new String object. If you create your own classes that return a (normally in your class private) String you'll probably want to create a new String out of them - as otherwise you pass the reference, and if it's modified afterwards you modify the private element that you initially wanted to protect...
But it's not really necessary here ;-)

allow thyself to be the spark that lights the fire
haslo@haslo.ch - www.haslo.ch​

 

[Savale]

Thank you much.. I actually got it late yesterday, I'm still a little used to programming in C++ still, and forget every once in a while. But thanks for all the help.