Builder pattern example, validation rule

gistfile1.txt

interface ValidationRule {
    /**
     * Return the error message for this validation rule,
     * which can be retrieved when validate is false.
     *
     */
    String getErrorMessage();
 
    /**
     * Execute the logic for this validation rule and return true
     * if valid and false if invalid.
     */
    boolean validate(String arg);
  }