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Wrapper types comparison doubt

Kedar Pethe
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Joined: Jul 17, 2012
Posts: 39
Chapter 6, Self test Q3.

Correct answers - B,C,D

How come answer is also D option??
I know that two Integer wrapper objects can be compared.

Using simple relational operator,
How can a short object be compared with an Integer object?
How does Java compare the two different wrapper's values??
Henry Wong
author
Sheriff

Joined: Sep 28, 2004
Posts: 18874
    
  40

Kedar Pethe wrote:Chapter 6, Self test Q3.

Correct answers - B,C,D

How come answer is also D option??
I know that two Integer wrapper objects can be compared.

Using simple relational operator,

How can a short object be compared with an Integer object?
How does Java compare the two different wrapper's values??


The answer is .... it depends.

If you are using a "==" or "!=" as the operator, it will do an instance comparison, meaning whether the two instances are the same instance.... and of course, this will fail to compile as Short and Integer are not sub/super classes of each other.

Otherwise, such as what you did in the example, it will do a value comparison, meaning it will unbox both sides first.

Henry


Books: Java Threads, 3rd Edition, Jini in a Nutshell, and Java Gems (contributor)
Kedar Pethe
Ranch Hand

Joined: Jul 17, 2012
Posts: 39
Henry Wong wrote:
If you are using a "==" or "!=" as the operator, it will do an instance comparison, meaning whether the two instances are the same instance.... and of course, this will fail to compile as Short and Integer are not sub/super classes of each other.
Otherwise, such as what you did in the example, it will do a value comparison, meaning it will unbox both sides first.
Henry


Ok.. but is it that while using >,<,<=,>= whatever be the two wrapper types(Byte,Short,Integer,Long,Float,Double) comparison will always take place on their values??
Kedar Pethe
Ranch Hand

Joined: Jul 17, 2012
Posts: 39
Henry Wong wrote:
If you are using a "==" or "!=" as the operator, it will do an instance comparison, meaning whether the two instances are the same instance.... and of course, this will fail to compile as Short and Integer are not sub/super classes of each other.

Otherwise, such as what you did in the example, it will do a value comparison, meaning it will unbox both sides first.

Henry

I tried, whatever be the two operands for relational operators, comparison always takes place on their values and gives correct output, without any error!!
 
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