generics question (sample mocks)

[Arjun Srivastava]

  
 import java.util.*;
 public class Main {
 public static void main(String[] args) {
 Set<Integer> set = new HashSet<Integer>();
Integer i1 = 45;
Integer i2 = 46;
 set.add(i1);
 set.add(i2);        System.out.print(set.size() + " ");
 set.remove(i1);     System.out.print(set.size() + " ");
 i2 = 47;            //line1
 set.remove(i2);     //line2
System.out.print(set.size() + " "+set);
}}

output:2 1 1 [46] ?
also if we commented out line 2 ,then again output is 2 1 1 [46] WHY and HOW?

[Neha Daga]

comment line 1 and compile the program. I think you will get your answer.

Also keep in mind wrapper classes are immutable.

[Arjun Srivastava]

Neha Daga wrote:comment line 1 and compile the program.

yes, if we commented out line 1
offcourse the output would be : 2 1 0 []
that is my question why in above code output is not 2 1 0 []?

[Neha Daga]

ok I will explain you line by line:

  
 import java.util.*;
 public class Main {
 public static void main(String[] args) {
 Set<Integer> set = new HashSet<Integer>();
Integer i1 = 45; 
Integer i2 = 46;
 set.add(i1);
 set.add(i2);   //line1     System.out.print(set.size() + " ");
 set.remove(i1);     System.out.print(set.size() + " ");
 i2 = 47;            //line2
 set.remove(i2);     //line3
System.out.print(set.size() + " "+set);
}}

After line1, set has 2 values 45 & 46 represented by i1 and i2.
Now, after line2, i2 now refers to 47 ans since wrapper objects are immutable it will be a new object and will not change the value of the object added to set.
Now, at line 3 you are trying to remove object refered by i2 i.e 47, which is not there in set so nothing will be removed from set and it will give the output:
2 1 1 [46]

Hope you understand.

[Arjun Srivastava]

naaice explanation.
i got it.
thanks for the quick reply.

[Neha Daga]

you are most welcome

[Ram Narayan.M]

Once the objects are added to the Set... It will be referred by the references in the Set... Here, you added Integer object having "46" to the set... That will be referred by reference in the Set...

In line1, i2 starts to refer to the Integer object "47". It does not mean that Integer object containing 46 will be changed to 47...

In line2, Integer object "47" is given to be removed... Search is made in the Set and removal does not occur since no Integer Object 47 is available...

So, the output is 46 and the size is retained as 1...

[amit mandal]

add this line instead of line 12:
System.out.println(set.remove(i2));

you will see that its returning false indicating that it is unable to find i2 with a value of 47. So confirming that 46 still remains in the collection and the rest of the explanation is same as its been told above.

[Arjun Srivastava]

yes amit you are right
thanks for reply here,
i got it.

[amit mandal]

You are welcome