Object Equality Use Equals

ID

java.object_equality_use_equals

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

CWE:480, reliability, suspicious-comparison

Description

Reports uses of == or != to compare two objects of a type that defines its own equals(). The identity operators test whether two references point to the same object in memory, not whether they are logically equal, leading to subtle bugs.

Rationale

The == operator checks reference identity, not logical equality. Two distinct objects that represent the same value will compare as not equal:

Money a = new Money(1000);
Money b = new Money(1000);
if (a == b) {             // false: different objects, although Money.equals says they are equal
    process();
}

This mistake is common when working with value objects, DTOs and entities.

Scope

The rule reports only when both operands resolve to a type declared in the analyzed project that defines its own equals(). Anything it cannot establish stays unreported, because an unresolved type is not evidence of a defect. In particular the following are never flagged:

  • null checks (a == null, a != null)

  • this on either side, which covers the if (this == o) return true; short-circuit at the head of an equals() implementation

  • enum comparisons (status == Status.ACTIVE) — == is the recommended idiom for enums

  • Class objects (type == String.class), which are canonical

  • primitives, boxed primitives and Object-typed operands

  • String comparisons — handled by the companion rule java.string_equality_use_equals

  • a class that does not define equals() at all, where identity is the only comparison available and therefore the intended one

  • any type declared outside the analyzed project. The project-wide software model does not index the JDK or third-party libraries, so for an imported type the rule can establish neither enum-ness nor an equals() override, and stays silent

Remediation

Use equals() (or Objects.equals() for null-safe comparison) for content equality:

Money a = new Money(1000);
Money b = new Money(1000);
if (a.equals(b)) {        // true: same value
    process();
}

References

© 2026 Xygeni. All rights reserved