?
Solved

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

Posted on 2009-04-07
3
Medium Priority
?
261 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 750 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

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

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

For beginner Java programmers or at least those new to the Eclipse IDE, the following tutorial will show some (four) ways in which you can import your Java projects to your Eclipse workbench. Introduction While learning Java can be done with…
Here is a helpful source code for C++ Builder programmers that allows you to manage and manipulate HTML content from C++ code, while also handling HTML events like onclick, onmouseover, ... Some objects defined and used in this source include: …
This theoretical tutorial explains exceptions, reasons for exceptions, different categories of exception and exception hierarchy.
This video teaches viewers about errors in exception handling.
Suggested Courses

719 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