Creating a custom validation

In some situations, we need our own special validation; for example, if we want to compare two fields, or if we want to validate some custom special component. In that case, we can add a custom validator and override the validate(Object) method. In this recipe, we will create a form for changing the password. We will add a custom validator that will match the new and confirmed password fields.

How to do it...

Carry out the following steps to create a form with a custom validation:

1. Create a Vaadin project with a main UI class called Demo.

   public class Demo extends UI {…}

2. We create a ChangePasswordForm class that is based on the FormLayout class.

   public class ChangePasswordForm extends FormLayout {…}

3. At first, we prepare some class fields. We create two instances of the PasswordField class for the new and confirmation password fields. In these fields, the characters are visually hidden. They are replaced by dots. Then we create the okButton object that will be used...