Conor Conor - 2 months ago 18
Java Question

Field Validation not working

I am new to

Java
. I have recently started my First project (Calculator) in Net beans.

While i was working on it I added a
if
condition to it.

The
if
condition checks whether the field is empty or not.

This is my code:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
double a, b, c;
a = Integer.parseInt(jTextField1.getText());
b = Integer.parseInt(jTextField2.getText());
if(jTextField1.getText().equals("")) {
jLabel2.setText("Please enter a number");
}
else {
c = a + b;
jLabel2.setText("" + c);
}
}


When I click the button with empty field it give me an error like this:

run:
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:504)
at java.lang.Integer.parseInt(Integer.java:527)
at calc.jButton1ActionPerformed(calc.java:132)
at calc.access$000(calc.java:11)
at calc$1.actionPerformed(calc.java:53)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3320)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)


But when i changed
if(jTextField1.getText().equals(""))
to
if(!jTextField1.getText().equals(""))
It worked correctly But when i add
else
condition to it The first part (Not == "") will work correctly. But second (else) will give error.

Please someone tell me how can i fix it?

Answer

Change your validation to occur before parsing the number:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    int a, b, c;
    if(jTextField1.getText().equals("")) {
        jLabel2.setText("Please enter a number");
    }
    else {
        a = Integer.parseInt(jTextField1.getText());
        b = Integer.parseInt(jTextField2.getText());
        c = a + b;
        jLabel2.setText("" + c);
    }
}

You may need also to check for other conditions, like is input a number. Putting text there will also throw NumberFormatException. I would change your validation logic to something like this:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    int a, b, c;

    try {
       a = Integer.parseInt(jTextField1.getText());
    } catch (NumberFormatException e) {
       jLabel2.setText("Please enter a number in field1");
       return;
    }

    try {
       b = Integer.parseInt(jTextField2.getText());
    } catch (NumberFormatException e) {
       jLabel2.setText("Please enter a number in field2");
       return;
    }

    c = a + b;
    jLabel2.setText("" + c);
}