Non-Standard equals() Signature

ID

java.equals_signature_correct

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

CWE:581, reliability

Description

Reports equals() methods whose signature does not match the standard public boolean equals(Object).

Rationale

To properly override Object.equals, the method must be public, return boolean, and accept a single parameter of type Object. A method with a narrower parameter type (e.g., equals(String)) overloads rather than overrides equals, so collections and framework code calling equals(Object) will still use the default identity comparison.

// Bad -- overloads instead of overriding
public class User {
    public boolean equals(User other) {  // wrong parameter type
        return this.id == other.id;
    }
}

Remediation

Change the signature to public boolean equals(Object) and add @Override to let the compiler enforce correctness.

// Good
public class User {
    @Override
    public boolean equals(Object other) {
        if (this == other) return true;
        if (!(other instanceof User)) return false;
        return this.id == ((User) other).id;
    }
}

References