Java Cart Validated java

package cart;

//Validated - interface which has a method isValid() to 
//        and a method getErrorMessage()
//        to return descruptive verbage if an object is not valid
//author - Lawrence Truett - FluffyCat.com
//date - August 18, 2003 - San Diego, CA
public interface Validated {
    
    public boolean isRequired();

    //return a boolean indicating if an object is valid. 
    public boolean isValid();
    
    //returns a boolean indicating if an object is null.
    public boolean isNull();

    //returns an error message
    public String getErrorMessage();
    
    //returns an error message, 
    //  including a message if nulls are not considered valid
    public String getErrorOrNullMessage();
        
    
}