What is the difference between Integer and int

[chaitanya karthikk]

Hi everybody, I am Chaitaya, I have read a topic regarding boxing and autoboxing in java. Then I got a doubt regardin the difference between Integer and java.

I searched the web, they said int is mutable and Integer is immutable, in the example which I was referring regarding autoboxing they changed the values of Integer object. So what should I believe.

You can find the explanations here boxing and autoboxing, difference between int and Integer

Thank you all in advance. Have a good day.

[Wouter Oet]

An Integer is immutable. Any operation that tries to change it value returns a new Integer object.
Try this:

final Integer value = Integer.valueOf(5);
value++;

It doesn't compile because value++ returns a new Integer object and tries to assign it to the value reference.
But because it's final it can't be changed.

[Seetharaman Venkatasamy]

one has identity, another doesnt have that.

[K Abhijit]

String is Imutable class:


People often get confused between FINAL and Immutable:: Just to clarify::

Final is : Constant Pointer:

 ..... final StringBuffer finalStrBReference = new StringBuffer("Java is nothing but SUN Technology");

now finalStrReference is Constant Reference (Pointer)...if you say

finalStrReference  =  new StringBuffer(" Now Java is owned by Oracle ") ;///

This would flag error , as once Memory address is assigned to Final Reference, it can not be changed...
You can not change the reference , but you CAN change the Object that reference is referring to...ie.

  finalStrReference .append(" Now Java is owned by Oracle ")  

IS ALLOWED


Immutable is Pointer to Constant :

 ..... String strReference ="Java is nothing but SUN Technology";

now strReference is normal Reference (Pointer)
if you say

strReference = new String("Now Java is owned by Oracle "); ///

This is allowed, but THIS ASSIGNMENT WOULD CREATE ANOTHER STRING OBJECT ON Heap and that memory address would be Assigned to reference strReference But the original Object "Java is nothing but SUN Technology" WOULD NEVER CHANGE (it might get Garbage Collected if there is no handle referring to it; but that's different story)

[K Abhijit]

Coming to your question:

Considering the concept of Final and Imuatble now you would find the difference.


int- mutable : - you can change the values of the int variable several times...

Interger Object: Imutable: The Object of Interger once Contructed CAN NEVER CHANGE IT'S STATE (like String )

Anyway, you should not compare Objects with Primitive datatypes...

[Campbell Ritchie]

chaitanya karthikk wrote: . . . int is mutable and Integer is immutable, . . .

That sounds misleading at best; where did you find it? An int is a primitive; it has no methods allowing you to change its state, just as no other primitive has any methods. I think "mutable" has no meaning for primitives. As you have been correctly told, you shouldn't compare objects with primitives.

But as you know you can say

int i = 123;
i = 345;

. . . unless i is marked as final. When you write i = i + j;, the JVM carries out an arithmetical calculation (i + j) and then assigns the result, by putting it into the memory location which you have called i. And you have had a nice demonstration of the difference between immutable and final from K Abhijit.

[chaitanya karthikk]

Wouter Oet wrote:An Integer is immutable. Any operation that tries to change it value returns a new Integer object.
Try this:

final Integer value = Integer.valueOf(5);
value++;

It doesn't compile because value++ returns a new Integer object and tries to assign it to the value reference.
But because it's final it can't be changed.

Hi Wouter, I did not understood the point you quoted. You have placed a final before the value object, so definitely one cannot change it, I write the following code.

public class Sample
{
	public static void main(String kk[])
	{
		Integer i=new Integer(10);
		i++;
		System.out.print(i);
	}
}

This is working fine, and however if I keep final before int i can make the integer variable also as immutable.

Please anyone clarify my doubt. Thank you all in advance.

[Wouter Oet]

What I was trying to demonstrate is that you can't change the value of an Integer object. This is what value++ means:

value gets unboxed to an int
that int is incremented
that int is then boxed and assigned to value.

But because value is final the reference can't be changed thus it doesn't compile.
In your example the Integer after the increment is not the same object as before the increment.

public class Sample   
{   
    public static void main(String kk[])   
    {   
        Integer i=new Integer(10); 
        System.out.println(System.identityHashCode(i));
        i++;   
        System.out.println(System.identityHashCode(i)); // Returns another number than before thus another object
        System.out.print(i);   
    }   
} 

[chaitanya karthikk]

Thank you Wouter for taking time and explaining me in a detailed manner. I am reading another article here. It is also nice and it explains both autoboxing and difference between int and Integer.

Thanks a lot.

[chaitanya karthikk]

Hi everybody, after reading all the posts I got a doubt, are String autoboxed?

Can I say "Strings are also autoboxed"?

Thank you all in advance.

[Campbell Ritchie]

chaitanya karthikk wrote: . . . Can I say "Strings are also autoboxed"? . . .

No.


It's nice to have an easy question occasionally

[chaitanya karthikk]

Thank you Ritche.

[K Abhijit]

@Chaitanya:

check your PM

[Rob Spoor]

K Abhijit, if the PM is relevant to this discussion please post it here. UseTheForumNotEmail also applies to PMs.

[K Abhijit]

@Rob : Point Noted

I posted one simple question to Chaitanya-
The reason I preferred to keep it private was:

Request (Chaitanya ) had got his answer to his Q (

Chaitanya karthikk wrote: . . . Can I say "Strings are also autoboxed"? . . .)

by Campbell

But instead of having it answered as YES / NO I was keen to make him think what it's got behind it....
Hence I posed it...

Q --> To which primitive type you can think String could be auto-boxed

[Campbell Ritchie]

K Abhijit wrote: . . . The reason I preferred to keep it private was: . . .

That was a useful point, which is why it ought not to be kept quiet.