Shift operators and bitwise shorthand assignments

1. Bit Shift Operators

• <<: Shift left.
• >>: Shift to the right.
• >>>: Unsigned right shift (with zero padding).

2. General Syntax of Shift Operators
value << num-bits: Shifts the value bits to the left.
value >> num-bits: Shifts the value bits to the right, preserving the sign bit.
value >>> num-bits: Shifts the value bits to the right, inserting zeros on the left.

3. Shift to the Left

• Each shift to the left causes all bits of the value to be shifted one position to the left.
• A 0 bit is inserted to the right.
• Effect: Multiplication of the value by 2 with each shift.

4. Shift to the Right

• Each right shift moves all bits one position to the right.
• The sign bit is preserved: 0 for positive values and 1 for negative values.
• Effect: Divide the value by 2 for each shift, with rounding down.

5. Shift to the Right No Signal (>>>)

• No preservation of the signal bit; inserts 0 on the left.
• Used in bit patterns where the value is treated as an unsigned number.

6. Displacement is not rotational

• Bits shifted out are lost.
• Shifting does not allow recovery of bits shifted out.

Example:
Scrolling Left and Right
*ShiftDemo *

Care when Shifting Byte and Short Values

• Java automatically promotes byte and short to int when evaluating an expression.

Example:

• Shifting a negative byte value to the right: when promoted to int, higher order bits are filled with 1.
• When shifting right with zero padding (>>>), this can cause problems as the top 24 bits will be 1 before zeros start to appear.

Abbreviated Assignments with Bitwise Operators

• All binary bitwise operators have a shorthand form that combines an assignment with the bitwise operation.

Example

x = x ^ 127; x ^= 127;

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