Question

I have a calculation application which I need to validate the fields to check if the values entered are numeric numbers and not alphanumeric. I have some ideas about the codes.
Please guide me if I have done anything wrong or seem noob as this is my first time trying out Swing.

private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {
    String text1 = jTextField1.getText();            // TODO add your handling code here:
}

private void jTextField2ActionPerformed(java.awt.event.ActionEvent evt) {
    String text2 = jTextField2.getText();        // TODO add your handling code here:
}

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    if (text1 and text2 != <numeric number>){
        JOptionPane.showConfirmDialog(null, "Please enter numbers only", "naughty", JOptionPane.CANCEL_OPTION);
    }
    // First we define float variables.
    float num1, num2, result;
    // We have to parse the text to a type float.
    num1 = Float.parseFloat(jTextField1.getText());
    num2 = Float.parseFloat(jTextField2.getText());
    // Now we can perform the addition.
    result = num1+num2;
    // We will now pass the value of result to jTextField3.
    // At the same time, we are going to
    // change the value of result from a float to a string.
    jTextField3.setText(String.valueOf(result));
    // TODO add your handling code here:
}

Please do help. By the way why does my NetBeans keep informing me that it does not recognize the “JOptionPane” Command?

Answer 1

Float.parseFloat() will throw a NumberFormatException if the String isn’t numeric and cannot be parsed into a Float. You can add a try-catch block to check for this condition:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
    float num1, num2, result;

    try {
        num1 = Float.parseFloat(jTextField1.getText());
        num2 = Float.parseFloat(jTextField2.getText());
        result = num1+num2;
        jTextField3.setText(String.valueOf(result));

    } catch (NumberFormatException e) {
        JOptionPane.showConfirmDialog(null, "Please enter numbers only", "naughty", JOptionPane.CANCEL_OPTION);
    }
}