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Wrapper classes?

Joe Harry
Ranch Hand

Joined: Sep 26, 2006
Posts: 9519
    
    2

The statements below,

Boolean b1 = Boolean.valueOf("True");
Boolean b2 = Boolean.valueOf("True");
System.out.println(b1 == b2); //prints true

Double d1 = Double.valueOf("10");
Double d2 = Double.valueOf("10");
System.out.println(d1 == d2);//prints false

Any reasons??


SCJP 1.4, SCWCD 1.4 - Hints for you, Certified Scrum Master
Did a rm -R / to find out that I lost my entire Linux installation!
Aniket Patil
Ranch Hand

Joined: May 02, 2006
Posts: 218
You have already asked this question here: http://www.coderanch.com/t/260776/java-programmer-SCJP/certification/Boolean-Wrappers

Also see http://www.coderanch.com/t/260471/java-programmer-SCJP/certification/Wrapper
[ December 21, 2006: Message edited by: Aniket Patil ]

SCJP 5.0 | SCWCD 1.4 <br /> <br />If you don't know where you are going, any road will take you there!
hemadri raju
Greenhorn

Joined: Mar 28, 2006
Posts: 15
In order to save memory, two instances of the
following wrapper objects will always be == when their primitive values are the same:
Boolean
Byte
Character from \u0000 to \u007f (7f is 127 in decimal)
Short and Integer from -128 to 127

hope that will help.
Burkhard Hassel
Ranch Hand

Joined: Aug 25, 2006
Posts: 1274
And what about this?

Long l = -128L;
Long m = -128L;
System.out.println(l==m);


Yours,
Bu


all events occur in real time
ramya ray
Ranch Hand

Joined: Aug 11, 2006
Posts: 101
is This applicable for 1.4 , as in my case below code is giving false...


Integer i = Integer.valueOf("1");
Integer j = Integer.valueOf("1");
System.out.println(i==j);

Kalpesh Jain
Ranch Hand

Joined: May 29, 2006
Posts: 30

And what about this?

Long l = -128L;
Long m = -128L;
System.out.println(l==m);


its clearly written at SCJP FAQs on javaranch

Note: The Java Language Specification does not explicitly guarantee this behavior for long values within the range of a byte.
[ December 21, 2006: Message edited by: Kalpesh Jain ]

Its a j a v a
Jim Yingst
Wanderer
Sheriff

Joined: Jan 30, 2000
Posts: 18671
[hemadri raju]: In order to save memory, two instances of the
following wrapper objects will always be == when their primitive values are the same:


Always?


"I'm not back." - Bill Harding, Twister
Maneeesh Saxena
Greenhorn

Joined: Dec 24, 2006
Posts: 26
hi all,
can you please mention the source from where to study above all.
is it part of SCJP1.4???
I've read K&B (SCJP1.4) but this is not covered there so please tell me the source for the same.
Regards
Prabhu Venkatachalam
Ranch Hand

Joined: Nov 16, 2005
Posts: 502

For SCJP 1.4 exam, whatever there in K&B book is fine.

If you want learn about wrapper classes. Lot of links available in SCJP FAQ


Prabhu Venkatachalam<br />SCJP 1.4,SCWCD 1.4<br />prabhu.venkatachalam@gmail.com
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: Wrapper classes?