Bitwise and Bit Shift operators in Java are powerful set of operators
which allows you to manipulate bits on integral types like int, long, short,
bytes and boolean data types in Java. Bitwise and Bit shift operator are among
the fastest operator in Java but still many Java programmers doesn't familiar
with bitwise and bitshift operations, especially those who doesn't come from C programming
backgrounds. If you have already learned C or C++ before starting with Java
then understanding bitwise and bitshift operators
are quite easy in Java, because its similar to bitwise operation in C. Some of
the tricky programming interview questions
e.g. checking if a number is power of two or swapping two numbers without temporary
variable or, can be easily solved using bitwise operators. This Java
programming tutorial is quick recap of different bitwise operator available in
Java and how to use them. This tutorial also discusses bit shift operator, both
signed and unsigned with example.
Basics
Before exploring bitwise and bit shift operator in Java, its prerequisite
that you must be familiar with binary format, bits, bytes and
bit wise operations like AND, OR, XOR, NOT etc. Knowledge of binary arithmetic
is also important to understand code written using bitwise operators in Java
programming language.
1) Binary format has just two bit, 0 and 1 and that's why is called binary.
2) In binary arithmetic :
0 + 0 = 0
0 + 1 = 1
1 + 1 = 10
3) Negation bitwise operation will change 0 to 1 and 1 to 0 and it’s
denoted by ~.
4) OR bitwise operation will return 1 if any of operand is 1 and zero
only if both operands are zeros.
5) AND bitwise operation will return 1 only if both operands are 1,
otherwise zero.
6) XOR bitwise operation will return 1 if both operands are different
e.g. one of them is 1 and other is zero and returns zero if both operands are
same e.g. 1,1 or 0,0
7) Integral types in Java (int, long, short and byte) are signed numbers
in Java where most significant bit (MSB) represent sign of number. 1 will
denote a negative number and 0 as MSB will denote a positive numbers
8) Negative numbers in Java are represented as 2's complement of number.
2's complement of a number is 1's complement + 1 and 1's complement means all
zero will turn to 1 and all 1 turned to zero in a binary number e.g. 1's
complement of 10 would be 01. and 2's complement of 10 would be 10+1 = 11 (all
in binary).
Bitwise operators in Java
Java provides several bitwise operator e.g. ~ for complement,
& for AND bitwise operation, | for OR
bitwise operation and ^ for bitwise XOR operation. All of these
operator implements there respective operation and operates on bit level. By
the way bitwise AND and OP operators are entirely different than logical AND && and
logical OR operators ||, which operates on boolean variables and also
implements AND and OR operation. Bitwise operator compares each bits of two
operands, for example if you apply bitwise AND operator & on two integers (
which is a 32 bit data type in Java),
bitwise AND will apply AND operation on
each bits of both operands.
Bitwise Operators Examples in Java
In this section we will see example of each of bitwise operator e.g.
bitwise negation or complement operator (~), bitwise AND (&), bitwise OR(|)
and bitwise XOR(^) operator in Java.
Bitwise
unary complement operator (~) Example
Bitwise unary complement operator changes bits from 0 to 1, or vice versa
and can only be applied on integral types. It’s not applicable on boolean
types.For example int variable contains 32 bits;
Applying this operator to a value whose bit pattern is 0000 would
change its pattern to 11111. Here is an example of bitwise
unary complement operator in Java :
int number = 2; //0010
//example of bitwise unary complement operator (~)
System.out.println(" value of number before: " + number);
System.out.println(" value of number after negation: " + ~number);
Output:
value of number before: 2
value of number after negation: -3
Bitwise
AND operator (&) Example
Bitwise AND operator works similar to logical AND operator (&&)
and returns 1 if both operands are 1. Difference with bitwise AND and logical
AND also known as short-circuit AND operator is that, logical AND operator
applies only to boolean type. Also bitwise AND operator is denoted by singe & while
short circuit AND operator is denoted by &&. If A
represent 0010 and B represent 1010 then result of A&B would be
0010. Here is another example of bitwise AND operator in Java
int a = 2; //0010
int b = 4; //0100
//example of bitwise AND operator &
System.out.println("Result of a&b
is " + (a&b)); //should be
zero
Output:
Result of a&b is 0
Bitwise
OR operator (|) Example
Bitwise OR operator is also similar to bitwise AND operator and applies
to individual bits. It’s different than short-circuit OR operator, which is
denoted by (||) and operates on boolean variable. Bitwise OR operator produce
result of OR operation on two bits as shown in below example. Like other
bitwise operator in Java, bitwise OR is only applicable to integral types.
int a = 2; //0010
int b = 4; //0100
System.out.println(" value of A bitwise OR B in Java : " + (a|b) );
Output:
value of A bitwise OR B in Java : 6
Bitwise
XOR operator (^) Example
Bitwise XOR operator is denoted by ^ and also work on individual bits.
There is no short-circuit XOR operator in Java and result of bitwise XOR
operator is XOR operation of individual bits. see the truth table of XOR
operation for predicting result. in short bitwise XOR operators will return 1
if both bits are different and return 0 if both bits are same. Bitwise XOR
operator also offers a nice trick to swap two numbers without using
temp variables. Here is a
code example of using bitwise XOR operator in Java:
int a = 2; //0010
int b = 4; //0100
System.out.println(" value of a XOR B in Java : " + (a^b) );
Output:
value of a XOR B in Java : 6
Bit Shift operator in Java- Example
Apart from bitwise operators, Java also provides bit shift operators,
which can be used to shift bit from one position to another on both left and
right side in a number. Java provides three bit shift operator signed left
shift operator "<<", signed
right shift operator ">>" and
unsigned right shift operator ">>>". Left
shift operator with sign, shifts bit into left side and fill the empty place
with zero, while right shift operator with sign, shifts the bit on right side
and fills the empty place with value of sign bit. For positive number it fills with zero and
for negative numbers it fills with 1. On the other hand ">>>" right
shift without sign operator will only shift the bit towards right without
preserving sign of number. As per syntax of bitshift operator, left hand side
of operand is the number whose bit needs to be shift and right hand side of
operator is how many bits needs to shift. This will be much clear with
following example of signed left shift, signed right shift and right shift
without sign operators:
public class BitShiftTest {
public static void main(String args[]) {
int number = 8; //0000 1000
System.out.println("Original number :
" + number);
//left shifting
bytes with 1 position
number = number<<1; //should be 16
i.e. 0001 0000
//equivalent of
multiplication of 2
System.out.println("value of number
after left shift: " + number);
number = -8;
//right shifting
bytes with sign 1 position
number = number>>1; //should be 16
i.e. 0001 0000
//equivalent of
division of 2
System.out.println("value of number
after right shift with sign: " + number);
number = -8;
//right shifting
bytes without sign 1 position
number = number>>>1; //should be 16
i.e. 0001 0000
//equivalent of
division of 2
System.out.println("value of number
after right shift with sign: " + number);
}
}
Output:
Original number : 8
value of number after left shift: 16
value of number after right shift with sign: -4
value of number after right shift with sign: 2147483644
From above example of bit shift operators in Java, you can imply that signed
left shift operators are equivalent of multiplying by 2 and signed right shift
operator with sign are dividing by two. I won’t suggest to do that in production quality code,
because it reduces readability.
Important
points to remember while using bit shift operators in Java
1. Smaller types like byte, short are
promoted to int before applying bit shift operator in Java. This
requires explicit casting on lower type of
result.
2. If number of shift positions exceeds with number of bits in a
variable, then remainder operator is used to calculate effective bit movement.
For example int variables contains 32 bit, and if you shift
bits to 33 times, then its equivalent of shifting bits 33%32 or just 1
time. e.g. 8 >> 33 is equal to 8 >> 1 and this is true for all bit shift operators.
3. Since bit shift operators can simulate divide by 2 and multiplied by 2
operation they can be used to implement fast multiplication and division but on
the cost of readability as its difficult to comprehend code written using bit
shift operators in Java.
That's all on bitwise and bit shift operators in Java. We have
seen basics and examples of different bitwise e.g. AND, OR and XOR and bitshift
operators such as right shift, left shift and right shift without sign. Java is
very rich in terms of bit wise operations and not only provides operators to
manipulate bits but also bit shift operator which can move bits on both left
and right direction. Only caveat of bitwise and bit shift operator is
readability but they are the first choice if you intend to do fast operations
in Java.
Related Java Programming articles from Javarevisited Blog
Source:http://javarevisited.blogspot.com/2013/03/bitwise-and-bitshift-operators-in-java-and-or-xor-left-right-shift-example-tutorial.html
Tidak ada komentar:
Posting Komentar