Difference between Bitwsie and Logical Operator in Java - & vs &&, | vs ||

Java beginners often ask same type of questions, and of them is what is difference between & and && operator in Java or difference between | and || operators? Standard answer of this question is well, main difference between & and && is that former is a bitwise operator and && is a logical operator in Java. That's academic, until you clearly explains difference in working of & and && or | and ||. For absolute beginners, & is used to represent AND logic operation in Java and | is used to represent OR logic operation. If we use only one & or | then it's known as “bitwise AND” and bitwise OR operators and if we use double && or || then it's known as logical or short-circuit AND and OR operators. From name, you can guess bitwise operates at bit level and perform AND logical operation to each bit, while logical operators operate on boolean variables only. Main difference lies in there short circuit behavior, which means if there are two or more conditions, which are joined using && or || operator then not all conditions are tested as soon as you have enough data to determine result. For example in case of AND operation involving multiple condition, rest are not checked as soon as one of them becomes false, because result will always be false. Similarly in case of OR short circuit operator ||, remaining conditions are not executed if one of them is true, because as soon as one operand becomes true, result of operation will be true, regardless of result of remaining condition. This short circuit nature is another reason, why logical operators are also known as short-circuit operator. In order to solve programming problems e.g. how to count number of set bits or 1s on Integer,  good understanding of bitwise operator is required.I think, we have enough theory, let's see some real examples.

& vs && and | vs || in Java

Let's first see examples of bitwise AND operator, as I said they operate at bit level and calculate AND for each bit in a number e.g. if we apply bitwise AND or & between two integer variable then there will be 32 AND operations as int is 32 bit in length. Similarly for byte it's 8 AND conditions and for short variables it's 16 AND operations.

int two = -2;
int four = -4;                          

int result = two & four; // bitwise AND operation

System.out.println(Integer.toBinaryString(two));
System.out.println(Integer.toBinaryString(four));
System.out.println(Integer.toBinaryString(result));

Output:
11111111111111111111111111111110
11111111111111111111111111111100
11111111111111111111111111111100

You can clearly see that for variable result, last two bits are off i.e. zero because of AND operations on respective bits of two and four int variable i.e . 0 & 0 = 0 , 1 & 0 = 0



Similarly, if we perform bitwise OR operation between these two variables, we will see following result.

result = two | four; // bitwise OR example

System.out.println(Integer.toBinaryString(two));
System.out.println(Integer.toBinaryString(four));
System.out.println(Integer.toBinaryString(result));

Output:
11111111111111111111111111111110
11111111111111111111111111111100
11111111111111111111111111111110

but using logical && and || operator on integral variables will result in compilation error.

int result = two && four; // Compilation Error

The operator && is undefined for the argument type(s) int, int





Similarly

int result = two || four; // Compilation Error

The operator || is undefined for the argument type(s) int, int





It means, you can only use bitwise AND and OR operators & and | with integral types in Java. Now let's see more interesting case of applying AND and OR operations on boolean types. This is where many Java programmers make mistake, as both & and && can be used with boolean variables. For example, what is difference between following two cases :

String address = person.getAddress();

if(address != null && address.length() > 0){
   send();
}

and

if(address != null & address.length() > 0){
   post(address);
}

This code snippet is checking if String is empty or not before calling post() method, though there are more clever ways to check if String is empty or not, this will do for our example. You will not notice any difference if address is not null, but as soon as address becomes null, second code snippet will start throwing java.lang.NullPointerException. Why? because && is short-circuit AND operator and doesn't execute address.length() if first condition is false e.g. when address is null, while & is bitwise AND operator and always execute address.length() > 0 expression, no matter whether address != null returns true or false. So you can now realize how & and && can make difference in your code, by the way using && for null check is another way to avoid NullPointerException in Java. Always use && instead of & if you don't want to check remaining conditions.

Difference between & and && in Java

It's time to revise whatever we learn so far. Also remember that there are far more bitwise operator than we discussed here, complete list is shown in this image, which also includes bitshift operators e.g. left shift, right shift and right shift without sign.

1) You can use & with both integral and boolean variables in Java, but you can use && with only boolean operands. Integral variables doesn't include floating point types e.g. float and double.





2) Bitwise AND & or bitwise OR | performs logical operation on all bits, while logical AND && and logical OR || abort executing remaining expression, as soon as result is determined. In best case short-circuit operator can return result by just executing one condition and in worst case by executing all conditions.





3) && and & is also known as conditional and unconditional AND operators in Java.





That's all about difference between bitwise and logical operator in Java. Remember logical operator is also known as short circuit operator in Java. In this tutorial we will learn that how & and && are different and how | is different than ||. Also remember that logical operator is only applicable for boolean operands but bitwise operator e.g. bitwise AND, OR, XOR and NOR can be applied to both boolean and integral type as well e.g. byte, short, char, int and long.



Some Programming problems based on bitwise operator :

1. How to swap two numbers without using temp variable? (solution)


2. How to find if number is even or odd? (solution)


3. How to add two numbers without using + operator in Java? (solution)


4. How to check if an integer is power of two in Java? (solution)

Source:http://javarevisited.blogspot.com/2015/01/difference-between-bitwsie-and-logical.html