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

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

Vulnerabilities Table of Contents


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


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


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