Question

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 another way to do this?

Answer 1

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")) {

}