Boxing,autoboxing,unboxing

[maddy saddy]

Anyone please explain Boxing,autoboxing and unboxing in detail.
I was unable get a clear cut view(even after reading K&B) on this topic.
I appreciate your help.
Thanks.

[marc weber]

Can you tell us specifically what your questions are? Are there certain code examples that you're questioning? (We could write a whole chapter going into detail... )

In the meantime, try this Autoboxing article.

[Chandra Bhatt]

Originally Posted By Maddy Saddy

Anyone please explain Boxing,autoboxing and unboxing in detail.
I was unable get a clear cut view(even after reading K&B) on this topic.
I appreciate your help.

We have primitive date types to work with but alas we were not allowed to work with Collection using primitive data types where objects are required.

What is Wrapper? : You know the class encapsulates member variables and methods to work on with, the same goes with wrapper, wrappers encapsulate
corresponding primitive data type. Boxing is simply meaning of encapsulating particular primitive to the corresponding class.

Integer i1 = new Interger(12);
Now i1 is a reference varaible that refers to a Integer wrapper object that encapsulates 12 (int primitive value).

We can use this Integer reference whereever Object is required to be use in the collections.

More enhanced facility: With Java 5.0 onwards we have one great facility and that is autoboxing. You need not to use new to create object of corresponding primitive; you simply write
Integer i1=12;
and that is equivalent to
Integer i1 = new Integer(12);
**Note except subtle issues related to creating wrapper Byte,Short,Character,Integer using new or compile time constant as you see
Integer i1 =12; //compile time constant

One exception : You may know integral wrappers I mentioneds above; if they encapsulate same value (within 127) they would give true in equality test. This is another issue.

Unboxing:
Integer i1 = new Integer(12);
int a = i1; //No problem, unboxing is done
Unboxing means, extract the primitive member value from the object;
In our case it is happening the same; 12 is extracted from the Integer object and assigned to primitive int a;

int a = i1; is equivalent to
int a = i1.intValue();
But who cares to do that when unboxing takes place automatically.

Boxing:
Integer i1 = new Integer(12);

Autoboxing:
Integer i1 = 12;

Unboxing:
int a = i1;


Hope this clarifies your doubts,
Thanks and regards,
cmbhatt

[maddy saddy]

Thanks alot Chandra.
Now the picture seems to be clear for me on boxing.