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Programmers frequently make errors regarding the precedence of operators because of the unintuitive unintuitively low - precedence levels of &, |, ^, <<, and >>. Avoid mistakes regarding precedence through the suitable use of parentheses. This , which also improves code readability unless taken to excess. The precedence of operations by the order of the subclauses are is defined in the Java Tutorials [Tutorials 20082013].

Although it advises against depending on parentheses for specifying evaluation order , EXP08EXP05-J. Do not write more than once to the same variable follow a write by a subsequent write or read of the same object within an expression applies only to expressions that contain side effects.

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The intent of the expression in this noncompliant code example is to add the variable OFFSET to the result of the bitwise logical AND between x and MASK.:

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public static final int MASK = 1337;
public static final int OFFSET = -1337;

public static int computeCode(int x) {
  return x & MASK + OFFSET;
}

According to the operator precedence guidelines, the expression is parsed as the following:

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x & (MASK + OFFSET)

This expression gets is evaluated , as follows, resulting in the value 0.:

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x & (1337 - 1337)

Compliant Solution

This compliant solution uses parentheses to ensure that the expression evaluates is evaluated as intended.:

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public static final int MASK = 1337;
public static final int OFFSET = -1337;

public static int computeCode(int x) {
  return (x & MASK) + OFFSET;
}

Exceptions

Noncompliant Code Example

In this noncompliant code example, the intent is to append either "0" or "1" to the string "value=":

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public class PrintValue {
  public static void main(String[] args) {
    String s = null;
    // Prints "1"
    System.out.println("value=" + s == null ? 0 : 1);
  }
}

However, the precedence rules result in the expression to be printed being parsed as ("value=" + s) == null ? 0 : 1.

Compliant Solution

This compliant solution uses parentheses to ensure that the expression evaluates as intended:

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public class PrintValue {
  public static void main(String[] args) {
    String s = null;
    // Prints "value=0" as expected
    System.out.println("value=" + (s == null ? 0 : 1));
  }
}

Applicability

Mistakes regarding precedence guidelines can cause an expression to be evaluated in an unintended way, which can lead to unexpected and abnormal program behavior.

EXP06-EX0: Parentheses may be omitted from mathematical expressions that follow the algebraic precedence rules. For instance, consider the following expression:

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x + y * z

By mathematical convention, multiplication is performed before addition; parentheses are redundant in this case.:

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x + (y * z)

Risk Assessment

Mistakes regarding precedence guidelines can cause an expression to be evaluated in an unintended way. This can lead to unexpected and abnormal program behavior.

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Guideline

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Severity

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Likelihood

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Remediation Cost

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Priority

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Level

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EXP06-J

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low

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probable

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medium

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P4

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Detection

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Detection of all expressions using low-precedence operators without parentheses is straightforward. Determining the correctness of such uses is infeasible in the general case; , although heuristic warnings could be useful.