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Wrapper class question ?

Sim Kim
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Joined: Aug 06, 2004
Posts: 268
Given that b and c refer to instances of wrapper classes, which two statements are true? (Choose two)

A. b.equals(b) returns true.
B. b.equals(c) returns the same result as b == c.
C. b.eqials(c) can return false even if c.equals(b) returns true.
D. b.equals(c) throws an exception if b and c are different wrapper types.
E. b.equals(c) returns false if the type of wrapper objects being compared are
Pradeep bhatt
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Joined: Feb 27, 2002
Posts: 8927

A, E is the answer. Hope that I have got it this time . :roll:
[missed A for the first time ]
[ January 12, 2005: Message edited by: Pradeep Bhat ]

Zak Guesmia

Joined: May 28, 2004
Posts: 21

SCJP1.4, SCWCD1.4, SCBCD1.3, SCDJWS, SCEA(part1), MCP, MCAD.NET, SCJP 5.0 (beta)
Pradeep bhatt
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Joined: Feb 27, 2002
Posts: 8927

B is not correct. Wrapper classes do override equals methods. StringBuffer,StringBuilder doesn't.
Vivek Mongolu
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Joined: Apr 17, 2003
Posts: 42
Wrapper classes override equals() method and return true if both the primitive values and the wrapper's classes are same.

page 384 of K&B book

so I guess teh answer is A and E.
Andris Jekabsons
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Joined: Jan 20, 2004
Posts: 82
Originally posted by rathi ji:
equals() method is only overridden in String class otherwise it is same as equally operator ( == )[ January 12, 2005: Message edited by: rathi ji ]

Check, for instance, equals() in Integer.
As I've noticed in other posts, I think you should brush up on the difference between "==" and "equals()". The first is used when referring to the same object in the memory by two references, the second when two different objects (occupying different memory locations) have equal values.
Mike Gershman
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Joined: Mar 13, 2004
Posts: 1272
For another interesting problem, change "equals(X)" to "compareTo(X)==0"

Mike Gershman
SCJP 1.4, SCWCD in process
I agree. Here's the link:
subject: Wrapper class question ?
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