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logical operators for AND and OR

 
Thomas Markl
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Posts: 192
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Hello,
I tried out a lot of comparisons with | and || and both
Had the same results.
So what is the difference beween | and || for the OR-Operator
And & and && for the AND-Operator.
I think | and || are the same and they are true if one expression is true.
When you put an AND by & or && both expressions have to be true.
So what is the difference between & and && => AND-Operation
Between | and || => OR-Operation???
int a = 3;
int b = 4;
if (a == 2 | b > 0 )
if (a ==2 || b >
if (a ==3 && b==2)
if (a == 3 & b==2)

Appreciate Your Answers.
Thomas
 
Dave Landers
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Posts: 401
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The || and && operators are "short cutting" operators. That is, as soon as the JVM can tell what the answer's going to be it stops. The | and & operators always evaluate everything.
The advantage is that you can do things like this:
if ( foo == null || foo.length() == 0 ) // etc
If foo is null, then the first part is true and no matter how the second part comes out the answer is always true. So the VM never will run "foo.length()" if foo is null.
If foo is non-null, it will go on to the length() test and see how that comes out.
So in the above case, you just can't get a NullPointerException.
But if you changed that to
if ( foo == null | foo.length() == 0 ) // etc
then you would get a NullPointerException if foo were null.
There are all kinds of uses for both kinds of operators, once you know how they work.
One other difference: Both kinds will do "boolean" tests, but only the | and & operators will do "bitwise" tests (and/or every bit in some number).
So 4 & 3 = 0 (in binary 0100 & 0011 = 0000)
4 | 3 = 7 (0100 | 0011 = 0111).
You can't do those sorts of things with && and ||.
 
Dirk Schreckmann
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Posts: 7023
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The || and && operators are sometimes called "short-circuiting" operators.
 
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