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

Posted on 2009-04-07
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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");

            }

    }

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Question by:chandanchoubey
  • 2
3 Comments
 
LVL 12

Accepted Solution

by:
basav_com earned 250 total points
Comment Utility
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();

	}
 

}

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Author Comment

by:chandanchoubey
Comment Utility
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
Comment Utility
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!
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