EXP51-JG. Do not perform assignments in conditional statements

Do not use the assignment operator in the outermost expression of an if or switch statement or a looping statement (while, do, or for) because it typically indicates programmer error and can result in unexpected behavior.

Noncompliant Code Example

In this noncompliant code example, an assignment expression is the outermost expression in an if statement.

public void f(boolean a, boolean b) {
  if (a = b) {
    /* ... */
  }
}

Although the intent of the code could be to assign b to a and test the value of the result, it is frequently a case of the programmer mistakenly using the assignment operator = instead of the equals operator ==.

Compliant Solution

When the assignment of b to a is unintended, this conditional block is now executed when a is equal to b.

public void f(boolean a, boolean b) {
  if (a == b) {
    /* ... */
  }
}

When the assignment is intended, the following compliant solution may be used because the programmer's intent is clearer:

public void f(boolean a, boolean b) {
  if ((a = b) == true) {
    /* ... */
  }
}

But it might be preferable to express this same logic as an assignment followed by a conditional:

public void f(boolean a, boolean b) {
  a = b;
  if (a) {
    /* ... */
  }
}

Risk Assessment

Errors of omission can result in unintended program flow.

Related Guidelines

Bibliography

EXP03-J. Do not use the equality operators when comparing values of boxed primitives