CODEWITHSUNDEEP
java
user277465
user277465

Reputation:

java bit shifting

I have the following line in my code :-

if (( checker & (1 << val)) ) return false;

where checker is of type int and val is of type int. When I try to compile the same I get the following :-

q11.java:38: incompatible types
found   : int
required: boolean
        if (( checker & (1 << val)) ) return false;
                      ^
1 error

However if I modify the code to have :-

if (( checker & (1 << val)) > 0 ) return false;

then I'm able to compile the source. I'm however unable to understand why the code did not work initially. Some pointers on why this happens?

Upvotes: 0

Views: 112

Answers (3)

Peter Lawrey
Peter Lawrey

Reputation: 533870

In Java, your condition must be a boolean i.e. true or false. It cannot be another type.

Your test should be as follow in case val == 31.

if ((checker & (1 << val)) != 0) return false;

BTW C doesn't have a boolean type as such. It uses an int value.

Upvotes: 2

P.P
P.P

Reputation: 121427

& is a unary which applied to a two integers (in your if condition) produces another integer. However, Java requires boolean values in conditions.

Upvotes: 3

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 727047

Unlike C and C++, where if takes integers (among many other types) and interprets zeros as false, Java requires boolean expressions in if, while, etc. Since & is an operation that produces an integer, your first expression is not valid in the condition of the if.

When you re-write C conditions like that in Java, you need to add != 0, not > 0. Otherwise, integers with the most significant bit set to 1 would fail your check.

Upvotes: 1

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