Using Primitive Wrapper Classes in Java

Question

Is there any difference between declaring the Integer below two ways

Integer Age = 25;
Integer Age = new Integer(25);

In the first case jvm caches the value, thus if `Integer Age=25; Intger b = 25; if(Age==b) will return true` — PermGenError, Apr 16 '13 at 11:12

Deepak Bala · Accepted Answer · 2013-04-16T11:17:44.270

8

The first integer is sourced from the Integer pool and the == check would return true

        Integer age = 25;
        Integer a = 25;
        System.out.println(a == age);

The 2nd one creates new objects every time and the == check would return false.

        Integer age = new Integer(25);
        Integer a = new Integer(25);
        System.out.println(a == age);

I have to add that only the integers through -128 -> 127 are cached by default, so the following snippet will return false too. You can tweak this by setting the property java.lang.Integer.IntegerCache.high to a value higher than 127 and it would return true.

        Integer age = 129;
        Integer a = 129;
        System.out.println(a == age);

edited Apr 16 '13 at 11:17

answered Apr 16 '13 at 11:12

Deepak Bala

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Thanks for Reply.But either way I am using wrapper classes right – Java Beginner Apr 16 '13 at 11:13
Yes you are using wrappers either way. The first declaration is a convenience method to get a pooled `Integer`. – Deepak Bala Apr 16 '13 at 11:14
In assigning Integer age = 25 autoboxing occurs by itself. Does autoboxing means converting to wrapper class by itself. – Java Beginner Apr 16 '13 at 12:13

score 1 · Answer 2 · answered Apr 16 '13 at 11:12

1

The first one uses autoboxing whilst the second one will create a new object every time. Its best if you can use Integer.valueOf() which will fetch from a local cache mainatained within the Integer class if it is already available within the cache.

answered Apr 16 '13 at 11:12

dinukadev

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score 0 · Answer 3 · answered Apr 16 '13 at 11:12

0

Yes!

Do NEVER use this line because it creates a duplicate object:

Integer Age = new Integer(25);

It is the same like using something like this:

String age = new String("old");

answered Apr 16 '13 at 11:12

sk2212

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score 0 · Answer 4 · answered Apr 16 '13 at 11:17

both are different we know that age is the reference variable and is stored in the stack 25 in the first line will be stored in the stack ,we can say that 25 is the address of the object in the heap u created in the second line and the heap value at the address location 25 is integer 25

Using Primitive Wrapper Classes in Java

4 Answers4