Assignment with Self-Increment

ID

java.assignment_with_self_increment

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

reliability, suspicious-comparison

Description

Reports statements of the form i = i++ or i = i-- where the self-assignment with post-increment is a no-op.

Rationale

Post-increment (i++) returns the value of i before incrementing. When that value is immediately assigned back to i, the increment is overwritten:

int i = 0;
i = i++;  // i is still 0 -- the increment is lost

int j = 5;
j = j--;  // j is still 5 -- the decrement is lost

This is one of the most common Java gotchas. The JVM first saves the old value, then increments, then assigns the saved old value back.

Remediation

Use plain increment or pre-increment:

i++;         // Simple post-increment
i = ++i;     // Pre-increment (returns the new value)
i = i + 1;   // Explicit addition

References