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The shift operators in Java have the following properties, according to The Java Language Specification (JLS), §15.19, "Shift Operators" [JLS 20052015]:

• The >> right shift is an arithmetic shift; the >>> right shift is a logical shift.
• The types boolean, float, and double cannot use the bit-shifting operators.
• When the value to be shifted is of type int, only the five lowest-order bits of the right-hand operand are used as the shift distance. That is, the shift distance is the value of the right-hand operand masked by 31 (0x1F). The shift distance actually used is consequently always in the range 0 to 31, inclusive.
• When the value to be shifted (left operand) is type long, only the last 6 bits of the right-hand operand are used to perform the shift. The shift distance is the value of the right-hand operand masked by 63 (0x3F). The shift distance actually used is consequently always in the range 0 to 63, inclusive.

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Arithmetic vs. Logical Shift

The JLS, §15.19 [JLS 20052015], defines the behavior of the arithmetic shift operator as follows:

The value of n>>s n>>s is n right-shifted s bit positions with sign-extension. The resulting value is ⌊ floor(n / 2^s ⌋). For nonnegative values of n, this is equivalent to truncating integer division, as computed by the integer division operator /, by two to the power s.

The JLS also defines the behavior of the logical shift operator:

The value of n>>>s n >>> s is n right-shifted s bit positions with zero-extension, where:

  • . If n is positive, then the result is the same as that of n>>s; if n >> s.

  • If n is negative and the type of the left-hand operand is int, then the result is equal to that of the expression (n>>sn >> s) + (2<<~s) if 2 << ~s).

  • If n is negative and the type of the left-hand operand is intlong, and to then the result is equal to that of the expression (n>>sn >> s) + (2L<<~s) if the type of the left-hand operand is long. 2L << ~s).

The added term (2<<~s2 << ~s) or (2L<<~s2L << ~s) cancels out the propagated sign bit.

(Note that, because of the implicit masking of the right-hand operand of a shift operator, ~s ~s as a shift distance is equivalent to 31-s when shifting an int value and to 63-s when shifting a long value.)

Never use the arithmetic shift operator when the logical shift operator is required.

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Incorrect use of shift operators can lead to unanticipated results, causing erratic control flow or unanticipated program behavior.

Automated Detection

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Tool	Version	Checker	Description
PVS-Studio	Include Page PVS-Studio_V PVS-Studio_V	V6034

Related Guidelines

Bibliography

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