Exception in thread "AWT-Eventqueue-0" java.lang.Numberformatexception: For input string: "8"

Question

I was developing a simple java application using Swing, and I don’t know what the error in my code.

Here follows the code:

private void btnVerificaActionPerformed(java.awt.event.ActionEvent evt) {                                            
    // TODO add your handling code here:
    int v = Integer.parseInt(txtValor.getText());
    if (v%2==0){
        lblResultado.setText("PAR");
    } else {
        lblResultado.setText("IMPAR");
    }

And the mistake:

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: " 8"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:569)
at java.lang.Integer.parseInt(Integer.java:615)
at classes.TelaParImpar.btnVerificaActionPerformed(TelaParImpar.java:88)
at classes.TelaParImpar.access$000(TelaParImpar.java:12)
at classes.TelaParImpar$1.actionPerformed(TelaParImpar.java:44)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
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:6533)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6298)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Answer 1

java.lang.Numberformatexception: For input string: "8"

The original string contains a space before the number 8.

You can solve the problem using the method trim, or, from Java 11, the method strip (the latter is Unicode-Aware):

int v = Integer.parseInt(txtValor.getText().trim());

It is worth however making your interface more robust so that the user can not enter anything but numbers. One of the possible solutions to this is to use a JFormattedTextField. Behold that answer in Soen for an example.