Object Model Violation: Just One of equals() and hashCode() Defined

From OWASP
Jump to: navigation, search

This is a Vulnerability. To view all vulnerabilities, please see the Vulnerability Category page.


This article includes content generously donated to OWASP by Fortify.JPG.

Last revision (mm/dd/yy): 02/20/2009

Vulnerabilities Table of Contents

Description

This class overrides only one of equals() and hashCode().

Java objects are expected to obey a number of invariants related to equality. One of these invariants is that equal objects must have equal hashcodes. In other words, if a.equals(b) == true then a.hashCode() == b.hashCode().

Failure to uphold this invariant is likely to cause trouble if objects of this class are stored in a collection. If the objects of the class in question are used as a key in a Hashtable or if they are inserted into a Map or Set, it is critical that equal objects have equal hashcodes.


Risk Factors

  • Talk about the factors that make this vulnerability likely or unlikely to actually happen
  • Discuss the technical impact of a successful exploit of this vulnerability
  • Consider the likely [business impacts] of a successful attack


Examples

The following class overrides equals() but not hashCode().

 public class halfway() {
   public boolean equals(Object obj) {
 	...
   }
 }

Related Attacks


Related Vulnerabilities

Related Controls


Related Technical Impacts


References

Note: A reference to related CWE or CAPEC article should be added when exists. Eg: