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The Java Lesson 7

Bitwise operations: overview with detailed examples

1. Logical bitwise operations
2. The complement operator
3. Bitwise shift operations
4. Bitwise assignment operations andr review questions

The complement operator

• Is unary (has a single operand)

• Uses the ~ operator to "flip" (reverse) the bits within an integer value. If a bit is "on" it is turned "off". If a bit is "off" it is turned "on".

For example, if

byte a = 17; // Binary value: 0001 0001 Hex value: 11
byte b;

after executing the statement

b = (byte) ~a;

variable b will have a value of -18 (because 0001 0001 reverses to 1110 1110). Once again, the cast is needed in order to store the int value that results from the operation.

Example: The following program can be run to test complement operations.

public class App {
public static void main(String[] args) {

// Variable to be read from the user

int number;

// Prompt for and read an integer value

System.out.print("Integer: ");
number = Keyboard.readInt();

// Display the result of complementing the number

System.out.println(" ~" + number + " = " + ~number);
}
}

Notes:

1. Again, program results are displayed in decimal so work them out in binary to understand what is happening.

2. The sign of a number changes when it is complemented due to the sign bit being reversed.

3. Be sure to run the program several times with different integer values.

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