Some Problem with Wrapper

[Mamta Sharma]

Question is from:-Valiveru's Mock Exam

Select the code segments(assuming is part of valid class) below that compile and run correctly with output: We are Equal



A.int i = 10;
long l = 10L;
if( i == l )
System.out.println("We are Equal");

B.int i = 10;
Integer ii = new Integer(10);
if( i == ii)
System.out.println("We are Equal");

C.int i = 10; char c = 10;
if( c == i)
System.out.println("We are Equal");

D.Integer ii = new Integer(10);
Integer jj = new Integer(10);
if(ii == jj)
System.out.println("We are Equal");

E.String s1 = "Null";
String s2 = "Null";
if( s1 == s2)
System.out.println("We are Equal");

F.String s1 = "Null";
String s2 = new String(s1);
if( s1 == s2)
System.out.println("We are Equal");

Correct answers are A,C,E
I agree with above answers.My confusion is with the option D,what i remember is if two Integer wrapper objects have the same values & between -128 to 127 then == operator returns true because they share the same location in memory.I tried to compile but no output is there.

Can anyone make it clear for me.

Thanks

Mamta

[Anit Nair]

Hi,

Thats true only if the two instances are created directly by assigning values directly i.e.

    
Integer i1=10;
Integer i2=20;
//Here both i1 and i2 point to same memory location i.e. same object

However,when you create two instance using the constructor, two different objects are created

  
Integer i1= new Integer(10);
Integer i2 = new Integer(10);
//Here i1 and i2 are two different object 

[Raphael Rabadan]

Integer in the range of -128 to 127 will be equal if created as literal. When you use new, no matter what object you are instantiating, you will have a new Object.

So, try it out:

Integer i1 = 10;
Integer i2 = 10;
Integer i3 = new Integer(10);
Integer i4 = new Integer(10);
 
System.out.println(i1==i2);
System.out.println(i3==i4);
System.out.println(i2==i3);

[Mamta Sharma]

Thanks Anit & Raphael,
I got it.

[Jarek Jankowski]

B is also a correct answer. Integer object is unboxed and comparison is made on two ints.

[Mamta Sharma]

Yes Jarek, you are right.