boolean bitwise problem

[gk]

code 1
======
boolean b1=true;
boolean b2=true;
System.out.println(b1|b2);

what does bitwise operator do for boolean variables...?How it works?





N.B

Lets look the following piece of code below...

byte b1=3; //011
byte b2=2; //010
System.out.println(b1|b2); //011 == 3

so this is basically doing bitwise OR operation,but i am in confusion
how it will calculate the similar for boolean type in (code 1),will u
please tell how it works?

 

[Pawel Szulc]

so this is basically doing bitwise OR operation,but i am in confusion
how it will calculate the similar for boolean type in (code 1),will u

have u tried to actually run it?

 

[lborupj]

Much like you would except:

b1 = true; b2=false; result= true;
b1 = false; b2=true; result= true;
b1 = true; b2=true; result= true;
b1 = false; b2=false; result= false;

simple OR

regards, Lars Borup Jensen
http://www.it-arbejde.dk


gk skrev:

 

[Patricia Shanahan]

code 1
======
boolean b1=true;
boolean b2=true;
System.out.println(b1|b2);

what does bitwise operator do for boolean variables...?How it works?

There is no bitwise | for boolean variables. The symbol "|" is
overloaded, representing two different operations:

1. If its operands are integers, it represents their bitwise or.

2. If its operands are booleans, it represents their logical or, true
if, and only if, at least one of b1 or b2 is true.

Patricia

 

[Lars Enderin]

Patricia Shanahan skrev:

There is no bitwise | for boolean variables. The symbol "|" is
overloaded, representing two different operations:

1. If its operands are integers, it represents their bitwise or.

2. If its operands are booleans, it represents their logical or, true
if, and only if, at least one of b1 or b2 is true.

The difference between || and | is that both operands are evaluated in
the single | case, but if the first operand (a) in (a || b) is true, the
second operand is not evaluated, which may avoid null references and
other side-effects.

 

[Patricia Shanahan]

Patricia Shanahan skrev:
The difference between || and | is that both operands are evaluated in
the single | case, but if the first operand (a) in (a || b) is true, the
second operand is not evaluated, which may avoid null references and
other side-effects.

All true, but why drag in "||" when the question was only about "|"?

Patricia

 

[Tor Iver Wilhelmsen]

2. If its operands are booleans, it represents their logical or, true
if, and only if, at least one of b1 or b2 is true.

In particular, the difference from || is that || "short-circuits"
while | doesn't (it evaluates both boolean expressions).

So:

"true||isFoo()" will NOT call isFoo(), while "true|isFoo()" will.

Same holds for & versus && of course.

 

[Chris Uppal]

All true, but why drag in "||" when the question was only about "|"?

Because without that difference in semantics between
boolean | boolean
and
boolean || boolean
there is no reason to have a specially overloaded meaning of | for booleans at
all.

-- chris

 

[gk]

There is no bitwise | for boolean variables. The symbol "|" is
overloaded, representing two different operations:

1. If its operands are integers, it represents their bitwise or.

2. If its operands are booleans, it represents their logical or, true
if, and only if, at least one of b1 or b2 is true.

Patricia

i liked these statements ...point 1 is ok and thats why i gave an byte
example for that ....but where from you get the point 2 ? is it in JLS
? your point 2 is probabily a valid explanation...and i guess that from
the output .....but i dont see any references anywhere which states
something like that ......have you found it anywhere ?

 

[Patricia Shanahan]

i liked these statements ...point 1 is ok and thats why i gave an byte
example for that ....but where from you get the point 2 ? is it in JLS
? your point 2 is probabily a valid explanation...and i guess that from
the output .....but i dont see any references anywhere which states
something like that ......have you found it anywhere ?

See the JLS, "15.22.2 Boolean Logical Operators &, ^, and |"
http://java.sun.com/docs/books/jls/second_edition/html/expressions.doc.html#5242,

"For |, the result value is false if both operand values are false;
otherwise, the result is true."

Patricia

 

[Chris Smith]

Because without that difference in semantics between
boolean | boolean
and
boolean || boolean
there is no reason to have a specially overloaded meaning of | for booleans at
all.

And because a lot of poor quality books and courseware, busy or
misinformed teachers, etc. continue to go about telling those who try to
learn Java that || is for booleans and | is for bitwise/integer
operations. Explicit misinformation sometimes needs to be corrected,
rather than merely ignored.