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Wiki Markup 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 also improves code readability, unless taken to excess. The precedence of operations by the order of the subclauses are defined in the Java Tutorials \[[Tutorials 2008|AA. Bibliography#Tutorials 08]\parentheses, which also improves code readability. The precedence of operations by the order of the subclauses is defined in the Java Tutorials [Tutorials 2013].

Although it advises against depending on parentheses for specifying evaluation order , guideline "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.

Noncompliant Code Example

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.:

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:

x & (MASK + OFFSET)

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

x & (1337 - 1337)

Compliant Solution

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

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

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

Noncompliant Code Example

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

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

Exceptions

}

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:

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:

x + y * z

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

x + (y * z)

...

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

Automated Detection

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.

Related Guidelines

C Coding Standard: "EXP00-C. Use parentheses for precedence of operation"

C++ Secure Coding Standard: "EXP00-CPP. Use parentheses for precedence of operation"

Bibliography

Automated Detection

Bibliography

...

EXP05-J. Use braces for the body of an if, for, or while statement      02. Expressions (EXP)      EXP07-J. Understand the differences between bitwise and logical operatorsImage Added Image Added Image Added