Data validation for preventing blank entries

Question

I want to create a validation wherein blank entries will not be accepted. So if I call this code:

entry[i].setName(JOptionPane.showInputDialog("Enter Name: "));
if the entry is blank, it will not be accepted and an error will prompt:

it cannot accept blank entries. Of course it could easily remedied with this code:

String name = JOptionPane.showInputDialog("Enter Name: ");
 while (name.equals("")){
       JOptionPane.showMessageDialog(null, "Cannot accept blank entries!");
       name = JOptionPane.showInputDialog("Enter Name: ");
 }

but if I want to validate 100 fields that I don't want to have a blank entry, then my code will be messy and long.

How could I do it better? I've read about using getters and setters or the try-catch methods to do the validation but I don't know if this kind of validation is applicable. And I don't know how I can do it. And if it is applicable, would I be violating the Model-View-Controller concept if I included a JOption message dialog box on my getter and setter methods? What code does programmers usually use in doing blank entries validation?

Answer 1

Extract the input code into a method:

String getNonBlankInput(String prompt) {
   String input = JOptionPane.showInputDialog(prompt);

   while (input.equals("")) {
      JOptionPane.showMessageDialog(null, "Cannot accept blank entries!");
      input = JOptionPane.showInputDialog(prompt);
   }

   return input;
}

Usage:

String name = getNonBlankInput("Enter name: ");

Answer 2

You should really look at the java validation standard, specifically JSR303.

Hibernate Validator is the reference implementation, take a look at their documentation.

To provide a simple example

public class Foo {
    @NotNull(message = "property bar must be provided")
    @Pattern(regexp = "[a-z0-9]", message = "property bar must contain only letters and numbers")
    private String bar;
}

ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
validator = factory.getValidator();

Foo foo = new Foo();

Set<ConstraintViolation<Foo>> constraintViolations = validator.validate(foo);
// now you have a Set of ConstraintViolations, if something is not working

Use the existing standards, no need to reinvent the wheel.

Answer 3

Please change the validating condition like this.

while ("".equals(input.trim())) {
      JOptionPane.showMessageDialog(null, "Cannot accept blank entries!");
      input = JOptionPane.showInputDialog(prompt);
}

This type of validation may also check only blanks as input & any other value also.

1. String name = JOptionPane.showInputDialog("Enter Name: "); contains spaces.
2. String name = JOptionPane.showInputDialog("Enter Name: "); contains null.