CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
Home > CWE List > CWE- Individual Dictionary Definition (2.11)  
ID

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

Weakness ID: 595
Abstraction: Base
Status: Incomplete
Presentation Filter:
+ Description

Description Summary

The program compares object references instead of the contents of the objects themselves, preventing it from detecting equivalent objects.
+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

Java

Language-independent

+ Common Consequences
ScopeEffect
Other

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.

+ Other 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.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory171Cleansing, Canonicalization, and Comparison Errors
Development Concepts699
ChildOfCategoryCategory569Expression Issues
Development Concepts (primary)699
ChildOfWeakness ClassWeakness Class697Insufficient Comparison
Research Concepts (primary)1000
ChildOfCategoryCategory847CERT Java Secure Coding Section 02 - Expressions (EXP)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory977SFP Secondary Cluster: Design
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness VariantWeakness Variant597Use of Wrong Operator in String Comparison
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
+ 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
Modifications
Modification DateModifierOrganizationSource
2008-07-01Sean EidemillerCigitalExternal
added/updated demonstrative examples
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Description, Relationships, Other_Notes
2009-05-27CWE Content TeamMITREInternal
updated Name
2010-12-13CWE Content TeamMITREInternal
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Relationships, Taxonomy_Mappings
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2014-06-23CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences
2014-07-30CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Incorrect Object Comparison: Syntactic
2009-05-27Incorrect Syntactic Object Comparison

More information is available — Please select a different filter.
Page Last Updated: May 05, 2017