- Consider using abstract classes if any of these
statements apply to your situation:
- You want to share code among several closely related
classes.
- You expect that classes that extend your abstract
class have many common methods or fields, or require access modifiers
other than public (such as protected and private).
- You want to declare non-static or non-final fields.
This enables you to define methods that can access and modify the state
of the object to which they belong.
- Consider using interfaces if any of these statements apply to your situation:
- You expect that unrelated classes would implement your
interface. For example, the interfaces Comparable and Cloneable are
implemented by many unrelated classes.
- You want to specify the behavior of a particular data
type, but not concerned about who implements its behavior.
- You want to take advantage of multiple inheritance of
type.
public interface Relatable {
// this (object calling isLargerThan)
// and other must be instances of
// the same class returns 1, 0, -1
// if this is greater than,
// equal to, or less than other
public int isLargerThan(Relatable other);
}
-----------------------------------------------
public Object findLargest(Object object1, Object object2) {
Relatable obj1 = (Relatable)object1;
Relatable obj2 = (Relatable)object2;
if ((obj1).isLargerThan(obj2) > 0)
return object1;
else
return object2;
}
https://docs.oracle.com/javase/tutorial/java/IandI/abstract.html
