Overriding a Method Using a Parameter That is a Subclass
abstract class Datum {
private Object value;
private Object name;
...
Datum(Object value) {
this.value = value;
}
Object getValue(){
return value;
}
abstract boolean lessThan(Datum d);
boolean greaterThanOrEqual(Datum d) {
return !lessThan(d);
}
}
class FloatDatum extends Datum {
FloatDatum(Float value) {
super(value);
}
boolean lessThan(FloatDatum fd){
return (((Float)getValue()).compareTo((Float)fd.getValue()) < 0);
}
boolean greaterThanOrEqual(FloatDatum fd) {
return super.greaterThanOrEqual((Float)fd.getValue());
}
}
Does FloatDatum.greaterThanOrEqual() override Datum.greaterThanOrEqual()? I am trying to enforce the rule that a FloatDatum object can only compare itself to another FloatDatum object. In other words I am trying to disallow comparing a FloatDatum to another object that subclasses Datum. I am hoping that by overriding greaterThanOrEqual() the superclasses' version of greaterThanOrEqual() cannot be called by a FloatDatum object and hence, a FloatDatum object will not be allowed to compare itself to any other object that subclasses Datum. I want to prevent the following from happening:
FloatDatum fd = new FloatDatum(new Float(3.0));
IntDatum id = new IntDatum(new Integer(2));
if(fd.lessThan(id)) {
....
}
Books and online info that I've read says that, to override a method you must supply the same parameter type in the method signature. Can you override by supplying a parameter that subclasses the parameter in the method that you want to override? After all, a FloatDatum object is a Datum.
