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Name the mutable and immutable Classes

Rashid Mian
Ranch Hand

Joined: Feb 14, 2007
Posts: 31
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
Ranch Hand

Joined: Oct 20, 2006
Posts: 43
As I know String and all the wrapper classes are immutable.
Rashid Mian
Ranch Hand

Joined: Feb 14, 2007
Posts: 31
Wrapper class are immutable? Can you explain with examples
Barry Gaunt
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Joined: Aug 03, 2002
Posts: 7729
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?


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sadasiva kumar
Ranch Hand

Joined: Oct 30, 2003
Posts: 91
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


SADASIVAKUMAR UTTI, SCJP1.4
A bend in the road is not the end of the road ... unless you fail to make the turn.
Ulf Dittmer
Marshal

Joined: Mar 22, 2005
Posts: 42916
    
  68
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
Ranch Hand

Joined: Aug 24, 2004
Posts: 80
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
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Joined: Mar 05, 2008
Posts: 3018
    
  10
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
Ranch Hand

Joined: Mar 05, 2008
Posts: 3018
    
  10
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
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Joined: Feb 19, 2008
Posts: 37
Why would you want to write a mutable class?
ramamohan gogula
Greenhorn

Joined: Mar 29, 2012
Posts: 3
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);
}
}
 
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