Name the mutable and immutable Classes

[Rashid Mian]

Can any body write in detail about the Mutable and Immutable classes that are commonly used. in Java and important wrt SCJP1.5

[Vishal K Patel]

As I know String and all the wrapper classes are immutable.

[Rashid Mian]

Wrapper class are immutable? Can you explain with examples

[Barry Gaunt]

What does it say in whatever book you are using to study for SCJP?
Have you looked at the java.lang package classes in the Java API?

[sadasiva kumar]

String(immutable) : Once we have assigned a value can never be change.It is immutable.
For example, we have String s = �abcdef�; //Create a new String
object,with value �abcdef� refers to it.
String s2 = s;//Create a 2nd reference variable
referring to the same thing.
s = s.contact(�morestuff�);//Create a new String
object,with value �abcdef morestuff� , refers
to it.
(Change s�s reference from the old string to
the new String.(Remember s2 is still referring to the original �abcdef� String.



StringBuffer(mutable): StringBuffer objects are changeable.It is mutable.
For example, StringBuffer sb = new StringBuffer(�abc�);
sb.append(�def�);
System.out.println(sb);
In this case the output will be �abcdef�.

regards
SADASIVAKUMAR UTTI

[Ulf Dittmer]

The wrapper classes for the primitives are immutable (Integer, Long, Character, etc.).

Wrapper classes per se are a concept that is orthogonal to mutability (i.e., they can be mutable or immutable).

[siva prakash]

Hi all,

how i will know whether class is mutable or not by seeing java api .

and how to create a mutable class of my own.




Thanks,
prakash

[Mike Simmons]

Originally posted by siva prakash:

how i will know whether class is mutable or not by seeing java api .

By using your memory? Vishal's first answer, as modified by Ulf, is probably all you need to know. You need to know what the primitive wrapper classes are anyway, because they come up in other parts of the test objectives (like autoboxing)
[ March 06, 2008: Message edited by: Mike Simmons ]

[Mike Simmons]

Originally posted by siva prakash:
and how to create a mutable class of my own.

Do you know how to create any class on your own?

Do you know what a mutable class is?

As Barry said above, what does it say in whatever book you are using to study for the SCJP?

[Tim Weide]

Why would you want to write a mutable class?

[ramamohan gogula]

Tim Weide wrote:Why would you want to write a mutable class?

if want to perform any modification on existing object with those changes a new Object will be created this concept is nothing but immutability......

sample code is

final public class MyImmutable{
private int var1=0;
public MyImmutable(int var1){
this.var1=var1;
}
public MyImmutable getModify(int var1){
if(this.var1==var1){return this;}
else
return new MyImmutable(var1);
}
}