How Does Right Shifting Work on Negative Numbers in Java?

What happens when you perform a right shift operation on a negative number in Java?

int num = -8; int shifted = num >> 1; // shifted will be -4

In Java, right shifting a negative number behaves differently compared to a positive number due to the way negative integers are represented in memory. Negative numbers are stored using two's complement notation. When a right shift operation is performed, Java uses an arithmetic right shift for signed numbers, which preserves the sign bit.

int num = -8; // Binary representation: 11111111 11111111 11111111 11111000
int shifted = num >> 1; // Result: -4, Binary: 11111111 11111111 11111111 11111100

Causes

• Negative numbers in Java are represented in two's complement form.
• The sign bit (leftmost bit) remains unchanged during an arithmetic right shift, ensuring the result retains its negative sign.

Solutions

• Use the logical right shift operator (>>>) if you want to shift bits right while filling the leftmost bits with zeros for a non-negative result.
• For operations that require consistent results regardless of the sign, consider using the absolute value of the number before shifting.

Mistake: Confusing arithmetic right shift (>>) with logical right shift (>>>) for negative numbers.

Solution: Always verify the type of right shift needed based on whether the number is signed or unsigned.

Mistake: Assuming that right shift will always halve the value of the number.

Solution: Understand that right shifting a negative number results in a lesser negative number, not exactly half.