Solved

How do I make a text field only to accept mathematical operators as first character of input.

Posted on 2009-04-07
3
256 Views
Last Modified: 2013-12-14
How do I make the text field to accept mathematical operators (+, -, *, /) only at char(0). nowhere else. My code lets the program accept the mathematical operators everywhere. Please check my code. I am using netbeans
private void txtNumberActionPerformed(java.awt.event.ActionEvent evt) {
        // Action Listner handling code here:
           if(txtNumber.getText().charAt(0) == '+' ||
              txtNumber.getText().charAt(0) == '-' ||
              txtNumber.getText().charAt(0) == '*' ||
              txtNumber.getText().charAt(0) == '/')
         {
     dataDisplay.append(txtNumber.getText()+ '\n');
     txtNumber.setText(null);
        }
         else
         {
      JOptionPane.showMessageDialog(null,"Sorry, " + txtNumber.getText() +
              " is not a valid entry" + "\n" + "Examples of valid Entry are:"
              + "\n" + "+23.5  " + "-1  " + "/6  " + " *12");
            }
    }

Open in new window

0
Comment
Question by:chandanchoubey
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
3 Comments
 
LVL 12

Accepted Solution

by:
basav_com earned 250 total points
ID: 24087112
Check this:

Use like this:
            if(txtNumber.getText().indexOf("+")> 0 || txtNumber.getText().indexOf("-")> 0 || txtNumber.getText().indexOf("*")> 0 || txtNumber.getText().indexOf("/")> 0 ){
/**
 * @(#)AcceptChars.java Created on Apr 7, 2009
 *
 * Copyright (c) 2007-2008 Subex, Ltd.
 * All Rights Reserved.
 *
 * This software is the confidential and proprietary information of
 * Subex Ltd ("Confidential Information"). You shall not disclose
 * such Confidential Information and shall use it only in accordance
 * with the terms of the license agreement you entered into
 * with Subex Ltd.
 */
 
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
 
/**
 * @author basaveswar.kureti
 *
 */
public class AcceptChars extends Frame implements TextListener {
	TextField txtNumber;
	AcceptChars(){
		txtNumber = new TextField(20);
		setLayout(new FlowLayout());
		add(txtNumber);
		setSize(500,400);
		setVisible(true);
		txtNumber.addTextListener(this);
		
	}
	
	public void textValueChanged(TextEvent  evt) {
        // Action Listner handling code here:
		if(txtNumber.getText().indexOf("+")> 0 || txtNumber.getText().indexOf("-")> 0 || txtNumber.getText().indexOf("*")> 0 || txtNumber.getText().indexOf("/")> 0 ){
			
   	      JOptionPane.showMessageDialog(null,"Sorry, " + txtNumber.getText() +
	              " is not a valid entry" + "\n" + "Examples of valid Entry are:"
	              + "\n" + "+23.5  " + "-1  " + "/6  " + " *12");
   	      String txt = txtNumber.getText();
   	       txtNumber.setText(txt.substring(0,txt.length()-1));
           }
		
 
	}
	
	public static void main(String args[]){
		new AcceptChars();
	}
 
}

Open in new window

0
 

Author Comment

by:chandanchoubey
ID: 24093241
Thanks basav_com. I appreciate your help. But if I input ++40 or --40. It accepts. I want only +40 or -40 to accept. If you can help me with this that will be great!
0
 

Author Closing Comment

by:chandanchoubey
ID: 31567454
Thanks basav_com. I appreciate your help. But if I input ++40 or --40. It accepts. I want only +40 or -40 to accept. If you can help me with this that will be great!
0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Programmer's Notepad is, one of the best free text editing tools available, simply because the developers appear to have second-guessed every weird problem or issue a programmer is likely to run into. One of these problems is selecting and deleti…
Introduction This article is the second of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article covers the basic installation and configuration of the test automation tools used by…
Viewers will learn about if statements in Java and their use The if statement: The condition required to create an if statement: Variations of if statements: An example using if statements:
The viewer will learn how to implement Singleton Design Pattern in Java.

627 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question