How elegantly make validation for the case when all fields in object are null?

I want to throw exception if all fields in object are null, but traditional way for checking on null looks not very smart. What can be 开发者_运维百科another way to do this?

EDIT : This uses reflection (java.lang.reflect.Field)

You could create a method within this object to return its valid state :

public boolean isValid() {
    boolean isValid = true;

    for (int i = 0; isValid && i < this.getClass().getFields().length; ++i) {
        if (this.getClass().getFields()[i].equals(null)) {
            isValid = false;
        }
    }

    return isValid;
}

This way, the method is going to validate each and every field of the class so you don't need to modifiy the code whenever you add a new field to it.

HOWEVER, the primary key cannot be null, so you have NOT to validate this field, or any NOTNULL field for that matter.

if (!field.getName().equals("aPrimaryKey_OR_aNotNullField")) {

}

Try this:

if (a == null && b == null && c == null) 
    throw new AllFieldsAreNullException();

You could potentially use reflection to write a generic method to analyse fields of an object, but it doesn't seem the clearest way of performing validation. I would perhaps be explicit for clarity's sake.