Please help me to know

Question

Hi friends,
I'm new to java, I have seen two programs like below. What is the difference? For both programs same result is comming.
import java.util.*;
class SetInterface{
public static void main(String args[]){
HashSet<Object> set = new HashSet<Object>();
set.add(new Integer(40));
set.add(new Integer(10));
set.add(new Integer(20));
set.add(new Integer(30));
System.out.println(set);
Output:
[30,40.20,10]
mport java.util.*;
class SetInterface{
public static void main(String args[]){
Set<Object> set = new HashSet<Object>(); // See here "I'm using Set Interface....What is the use"
set.add(new Integer(40));
set.add(new Integer(10));
set.add(new Integer(20));
set.add(new Integer(30));
System.out.println(set);
Output:
[30,40.20,10]

Answer 1

ravindra.alld wrote:
here the super class object is refering to the subclass object.Totally wrong.
-- There's no "super class" involved, Set is an interface, not a class.
-- Objects don't refer to objects. Variables reference objects.
@OP: In the second case, the rest of the method is independent of what implementation of Set you use. so in the face of any changing requirement, you could use a ConcurrentSkipListSet / LinkedHashSet / any other kind of Set without changes to the rest of the code.
This assumes greater importance when the code is long and possibly cumbersome to trace through, or the Set is the return value from a method.
The principle I follow is to code to the Interface or Class that provides the method(s) I intend to use. In your case, you are not using any functionality that is specific to HashSet, so I would go with declaring the variable as a Set.
db