Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

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CWE-595: Comparison of Object References Instead of Object Contents

Weakness ID: 595
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The program compares object references instead of the contents of the objects themselves, preventing it from detecting equivalent objects.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
ChildOfClassClass697Insufficient Comparison
ParentOfVariantVariant597Use of Wrong Operator in String Comparison
+ Relevant to the view "Development Concepts" (CWE-699)
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Java (Undetermined Prevalence)

Class: Language-Independent (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.


Technical Impact: Other; Varies by Context

This weakness can lead to erroneous results that can cause unexpected application behaviors.
+ Demonstrative Examples

Example 1

In the example below, two Java String objects are declared and initialized with the same string values and an if statement is used to determine if the strings are equivalent.

(bad code)
Example Language: Java 
String str1 = new String("Hello");
String str2 = new String("Hello");
if (str1 == str2) {
System.out.println("str1 == str2");


However, the if statement will not be executed as the strings are compared using the "==" operator. For Java objects, such as String objects, the "==" operator compares object references, not object values. While the two String objects above contain the same string values, they refer to different object references, so the System.out.println statement will not be executed. To compare object values, the previous code could be modified to use the equals method:

(good code)
if (str1.equals(str2)) {
System.out.println("str1 equals str2");


Example 2

In the following Java example, two BankAccount objects are compared in the isSameAccount method using the == operator.

(bad code)
Example Language: Java 
public boolean isSameAccount(BankAccount accountA, BankAccount accountB) {
return accountA == accountB;


Using the == operator to compare objects may produce incorrect or deceptive results by comparing object references rather than values. The equals() method should be used to ensure correct results or objects should contain a member variable that uniquely identifies the object.

The following example shows the use of the equals() method to compare the BankAccount objects and the next example uses a class get method to retrieve the bank account number that uniquely identifies the BankAccount object to compare the objects.

(good code)
Example Language: Java 
public boolean isSameAccount(BankAccount accountA, BankAccount accountB) {
return accountA.equals(accountB);

+ Potential Mitigations

Phase: Implementation

Use the equals() method to compare objects instead of the == operator. If using ==, it is important for performance reasons that your objects are created by a static factory, not by a constructor.
+ Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
MemberOfCategoryCategory847CERT Java Secure Coding Section 02 - Expressions (EXP)
MemberOfViewView884CWE Cross-section
MemberOfCategoryCategory977SFP Secondary Cluster: Design
+ Notes


This problem can cause unexpected application behavior. Comparing objects using == usually produces deceptive results, since the == operator compares object references rather than values. To use == on a string, the programmer has to make sure that these objects are unique in the program, that is, that they don't have the equals method defined or have a static factory that produces unique objects.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CERT Java Secure CodingEXP02-JUse the two-argument Arrays.equals() method to compare the contents of arrays
CERT Java Secure CodingEXP02-JUse the two-argument Arrays.equals() method to compare the contents of arrays
CERT Java Secure CodingEXP03-JDo not use the equality operators when comparing values of boxed primitives
+ Content History
Modification DateModifierOrganization
2008-07-01Sean EidemillerCigital
added/updated demonstrative examples
2008-07-01Eric DalciCigital
updated Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Description, Relationships, Other_Notes
2009-05-27CWE Content TeamMITRE
updated Name
2010-12-13CWE Content TeamMITRE
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Common_Consequences, Demonstrative_Examples, Relationships, Taxonomy_Mappings
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2014-06-23CWE Content TeamMITRE
updated Applicable_Platforms, Common_Consequences
2014-07-30CWE Content TeamMITRE
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Incorrect Object Comparison: Syntactic
2009-05-27Incorrect Syntactic Object Comparison

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Page Last Updated: January 18, 2018