Bitwise Operators

In the second lesson on operators we look at the bitwise logical and bitwise shift operators. Bitwise operators perform their operations on the integer types byte, short, int and long and will not work with any other type. These operators are used to manipulate the bits within an integer value, hence the name.
·Bits with the value 0 are said to be switched off.
·Bits with the value 1 are said to be switched on.
·All bitwise conversions get promoted to the int type before conversion so you need to cast back to short and byte when using these types for the target.
Bitwise Logical Operators Top
The bitwise logical operators perform the same operations as the logical operators discussed in the last lesson but work on a bit-by-bit basis on the integer type. The following table shows all possible combinations for a bit using 0 and 1.
Operator
Meaning
Example
Result
Notes
&
AND
bit a = 0 and bit b = 0
a & b
bit a = 0 and bit b = 1
a & b
bit a = 1 and bit b = 0
a & b
bit a = 1 and bit b = 1
a & b

0

0

0

1
Will turn the result bit to 0 unless both bits are 1.

Useful for switching bits off.
|
OR
bit a = 0 and bit b = 0
a | b
bit a = 0 and bit b = 1
a | b
bit a = 1 and bit b = 0
a | b
bit a = 1 and bit b = 1
a | b

0

1

1

1
Will turn the result bit to 1 if either bits are 1.

Useful for switching bits on.
^
XOR (exclusive OR)
bit a = 0 and bit b = 0
a ^ b
bit a = 0 and bit b = 1
a ^ b
bit a = 1 and bit b = 0
a ^ b
bit a = 1 and bit b = 1
a ^ b

0

1

1

0
Will switch the result bit to 1 if only one of the bits is 1 otherwise the result bit is switched to 0.

Useful for highlighting unmatched bits.
~
NOT
bit a = 0
~a
bit a = 1
~a

1

0
Useful for switching bits to show the compliment of the number.
Let’s look at each of the bitwise logical operators in turn to get a feel for how they work.
Bitwise AND Top
The bitwise AND operator can be used for turning non-matched bits off. Lets look at some code to illustrate how this works:

/*
Bitwise AND
*/
public class BitwiseAnd {

public static void main (String[] args) {
byte a = 97;
printBits(a);
byte b = 57;
printBits(b);
byte c = (byte) (a & b);
printBits(c);
}

/*
Method to loop through input parameter and print out the bits
*/
static void printBits (byte aByte) {
System.out.print(“Input param aByte = ” + aByte + “: “);
for (int i = 128; i > 0; i /= 2) {
if ((aByte & i) != 0) {
System.out.print(“1 “);
} else {
System.out.print(“0 “);
}
}
System.out.println(” “);
}
}

Save, compile and run the file in directory   c:_BeginningJava6

Ok there are several new things going on with the above piece of code that we will go through. The first thing to notice is we are casting to a byte when using the bitwise AND (byte c = (byte) (a & b);). All bitwise conversions get promoted to the int type before conversion so we need to cast back to the byte type. Also we are enclosing the bitwise operation in parentheses so the whole expression gets evaluated and not just the a. We are using the printBits method to save replication of code. We pass each variable to this method and print the value. We then use a for loop to print out each bit of the byte variable passed to the method. We will go through the for loop in the Loop Statements lesson but what we are doing here is just dividing 256 by 2 to get to each bit. The 8th bit is used for the sign (0 = positive, 1 negative), hence the actual value range of a byte is 127 to -128 as stated in the Primitive Variables lesson. As you can see from the output the bitwise AND operator switches non-matched bits off.
Bitwise OR Top
The bitwise OR operator can be used for turning non-matched bits on. Lets look at some code to illustrate how this works:

/*
Bitwise OR
*/
public class BitwiseOr {

public static void main (String[] args) {
byte a = 97;
printBits(a);
byte b = 57;
printBits(b);
byte c = (byte) (a | b);
printBits(c);
}

/*
Method to loop through input parameter and print out the bits
*/
static void printBits (byte aByte) {
System.out.print(“Input param aByte = ” + aByte + “: “);
for (int i = 128; i > 0; i /= 2) {
if ((aByte & i) != 0) {
System.out.print(“1 “);
} else {
System.out.print(“0 “);
}
}
System.out.println(” “);
}
}

Save, compile and run the file in directory   c:_BeginningJava6

As you can see from the output the bitwise OR operator switches non-matched bits on.
Bitwise XOR Top
The bitwise XOR operator can be used for highlighting unmatched bits as any matching bits will be switched to 0, whilst unmatched bits are switched to 1. Lets look at some code to illustrate how this works:

/*
Bitwise XOR
*/
public class BitwiseXor {

public static void main (String[] args) {
byte a = 97;
printBits(a);
byte b = 57;
printBits(b);
byte c = (byte) (a ^ b);
printBits(c);
}

/*
Method to loop through input parameter and print out the bits
*/
static void printBits (byte aByte) {
System.out.print(“Input param aByte = ” + aByte + “: “);
for (int i = 128; i > 0; i /= 2) {
if ((aByte & i) != 0) {
System.out.print(“1 “);
} else {
System.out.print(“0 “);
}
}
System.out.println(” “);
}
}

Save, compile and run the file in directory   c:_BeginningJava6

As you can see from the output the bitwise XOR operator switches non-matched bits on and matched bits off.
Bitwise NOT Top
The bitwise NOT operator can be used for switching bits to show the compliment of the number. Lets look at some code to illustrate how this works:

/*
Bitwise NOT
*/
public class BitwiseNot {

public static void main (String[] args) {
byte a = 57;
printBits(a);
a = (byte)~a;
printBits(a);
}

/*
Method to loop through input parameter and print out the bits
*/
static void printBits (byte aByte) {
System.out.print(“Input param aByte = ” + aByte + “: “);
for (int i = 128; i > 0; i /= 2) {
if ((aByte & i) != 0) {
System.out.print(“1 “);
} else {
System.out.print(“0 “);
}
}
System.out.println(” “);
}
}

Save, compile and run the file in directory   c:_BeginningJava6

As you can see from the output the bitwise NOT operator switches bits to show the compliment of the number.
Bitwise Shift Operators Top
The bitwise shift operators allow us to shift the bits that make up an integer type to the left or right by a specified amount.
Operator
Meaning
Example
Result
Notes
<< Left shift int a = 1234; a = a << 2; 4936 Will shift the value by the specified number of bits to the left. value << numberOfBits. >>
Right shift
int a = 1234; a = a >> 3;
154
Will shift the value by the specified number of bits to the right.

value >> numberOfBits.
>>>
Signed right shift
int a = -12345; >>> 4;
-772
Will shift the value by the specified number of bits to the right, whilst retaining the signed bit.

If the value is negative then the resultant moved bits will be sign-extended.

value >>> numberOfBits.
Let’s look at each of the bitwise shift operators in turn to see how we got the values in the table above.
Bitwise Left Shift Top
The bitwise left shift operator allows us to shift the bits in an integer type to the left by the specified amount.

/*
Bitwise Left Shift
*/

public class BitwiseLeftShift {

public static void main (String[] args) {
short a = 1234;
printBits(a);
a = (short) (a << 2); printBits(a); } /* Use a loop to print out the bits */ static void printBits (short aShort) { System.out.print("Input param aShort = " + aShort + ": "); for (int i = 32768 ; i > 0; i /= 2) {
if (i == 128) {
System.out.print(” | “);
}
if ((aShort & i) != 0) {
System.out.print(“1 “);
} else {
System.out.print(“0 “);
}
}
System.out.println(” “);
}
}

Save, compile and run the file in directory   c:_BeginningJava6

As you can see from the output all the bits have been shifted 2 places to the left giving us a new value. We are using the | symbol to split the result into 8-bit chunks.
Bitwise Right Shift Top
The bitwise right shift operator allows us to shift the bits in an integer type to the right by the specified amount.

/*
Bitwise Right Shift
*/

public class BitwiseRightShift {

public static void main (String[] args) {
short a = 1234;
printBits(a);
a = (short) (a >> 3);
printBits(a);
}

/*
Use a loop to print out the bits
*/
static void printBits (short aShort) {
System.out.print(“Input param aShort = ” + aShort + “: “);
for (int i = 32768 ; i > 0; i /= 2) {
if (i == 128) {
System.out.print(” | “);
}
if ((aShort & i) != 0) {
System.out.print(“1 “);
} else {
System.out.print(“0 “);
}
}
System.out.println(” “);
}
}

Save, compile and run the file in directory   c:_BeginningJava6

As the output shows all the bits have been shifted 3 places to the right giving us a new value. We are using the | symbol to split the result into 8-bit chunks.
Bitwise Signed Right Shift Top
The bitwise signed right shift operator allows us to shift the bits in an integer type to the right by the specified amount, whilst retaining the signed bit.

/*
Bitwise Signed Right Shift
*/

public class BitwiseSignedRightShift {

public static void main (String[] args) {
short a = -12345;
printBits(a);
a = (short) (a >>> 4);
printBits(a);
}

/*
Use a loop to print out the bits
*/
static void printBits (short aShort) {
System.out.print(“Input param aShort = ” + aShort + “: “);
for (int i = 32768 ; i > 0; i /= 2) {
if (i == 128) {
System.out.print(” | “);
}
if ((aShort & i) != 0) {
System.out.print(“1 “);
} else {
System.out.print(“0 “);
}
}
System.out.println(” “);
}
}

Save, compile and run the file in directory   c:_BeginningJava6

As the output shows all the bits have been shifted 3 places to the right giving us a new value. We are using the | symbol to split the result into 8-bit chunks.
Did you spot anything else? When you right shift a negative number, when the interim expression is promoted to an int from a short or byte all the extra bits are sign-extended. Thus when we cast back to a short in our example all bits shifted in after our signed bit are 1 and we get an unexpected result. Be aware of this when using this particular bitwise operator.
Bitwise Shorthand Assignment Operators Top
The bitwise shorthand assignment operators allow us to write compact code that is implemented more efficiently. When using the bitwise shorthand assignment operators there is no need to cast either.
Operator
Meaning
Example
Result
Notes
&=
Bitwise AND
byte a = 74; a &= 124;
72
Will give the Bitwise AND result of 74 and 124.
|=
Bitwise OR
byte a = 74; a |= 124;
126
Will give the Bitwise OR result of 74 and 124.
^=
Bitwise XOR
byte a = 74; a ^= 124;
54
Will give the Bitwise XOR result of 74 and 124.
<<= Left shift short a = 1234; a <<= 2; 4936 Left shift 1234 by 2 bits. >>=
Right shift
short a = 1234; a >>= 3;
154
Right shift 1234 by 3 bits.
>>>=
Signed right shift
short a = -12345; a >>>= 4;
-772
Signed right shift -12345 by 4 bits.
Operator Precedence Top
We will finish our discussion on operators with a table showing the order of precedence that is invoked when Java interprets operator symbols. The list includes the special operators which will be discussed in later lessons. When using multiple operators in an expression it is always best practice to use parentheses to explicitly state the order of precedence for clarity and readability. The table lists order of precedence from highest to lowest.
Precedence
Operators
Operation
Associativity
1
()
method call
left

[ ]
array index

.
method access

2
+
unary plus
right


unary minus

++
prefix/postfix increment


prefix/postfix decrement

!
boolean logical NOT

~
bitwise NOT

(type)
type cast

new
object creation

3
/
division
left

*
mutiplication

%
modulus

4
+
addition or string concatenation
left


subtraction

5
<< bitwise left shift left >>
bitwise right shift

>>>
bitwise signed right shift

6
< less than left <= less than or equal to >
greater than

>=
greater than or equal to

instanceof
reference test

7
==
equal to
left

!=
not equal to

8
&
boolean logical AND or bitwise AND
left
9
^
boolean logical XOR or bitwise XOR
left
10
|
boolean logical OR or bitwise OR
left
11
&&
short-circuit boolean logical AND
left
12
||
short-circuit boolean logical OR
left
13
? :
conditional
right
14
=
assignment
right

+=
shorthand addition

-=
shorthand subtraction

/=
shorthand division

*=
shorthand mutiplication

%=
shorthand modulus

&=
shorthand boolean logical AND or bitwise AND

|=
shorthand boolean logical OR or bitwise OR

^=
shorthand boolean logical XOR or bitwise XOR

<<= shorthand bitwise left shift >>=
shorthand bitwise right shift

>>>=
shorthand bitwise signed right shift

Bitwise Operators Quiz Top
Try the quiz below to test your knowledge of this lesson
Question 1 : What symbol do we use for the bitwise AND operation?
·~
·&
·^
·|
– We use the & symbol for the bitwise AND operation.
Next >>
Question 2 : What is the bitwise OR useful for?
·Showing the compliment of the number
·Showing unmatched bits
·Switching bits off
·Switching bits on
– The bitwise OR is useful for switching bits on.
<< Prev Next >>
Question 3 : We can use bitwise operators on any primitive type?
·true
·false
– The bitwise operators only work with the integer types (byte, short, int and long).
<< Prev Next >>
Question 4 : Which of the following is the symbol for the bitwise signed right shift?
·>>
·<< ·>>>
– >>> is the symbol for the bitwise signed right shift.
<< Prev Next >>
Question 5 : What value do bits have that are said to be swiched on?
·0
·1
– Swiched on bits have the value 1.
<< Prev Next >>
Question 6 : What bitwise shift operator retains the sign?
·>>>
·<< ·>>
– The bitwise signed operator (>>>) retains the sign. In fact all bits shifted into the target will be signed.
<< Prev Finish! Status Bar Please select an answer What's Next? In this lesson we look at the conditional statements available in Java. <<  Operators                    Conditional Statements  >>
 Java6 Tutor Homepage  Top
All the Beginning Java6 lessons are listed below. Click a link to go to that lesson.

Beginning Java6
Getting Started
Code Structure & Syntax
Primitive Variables
Method Scope
Operators
Bitwise Operators
Bitwise Logical Operators
Bitwise AND
Bitwise OR
Bitwise XOR
Bitwise NOT
Bitwise Shift Operators
Bitwise Left Shift
Bitwise Right Shift
Bitwise Signed Right Shift
Shorthand Assignment Operators
Operator Precedence
Bitwise Operators Quiz
Conditional Statements
Loop Statements
 

 

Aly Chiman

Aly Chiman is a Blogger & Reporter at AlyChiTech.com which covers a wide variety of topics from local news from digital world fashion and beauty . AlyChiTech covers the top notch content from the around the world covering a wide variety of topics. Aly is currently studying BS Mass Communication at University.

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