Details
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Type:
Bug Detection
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Status: Active
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Resolution: Unresolved
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Labels:None
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Message:Add a "hashCode()" method to "className" or remove it from this hash.
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Default Severity:Major
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Impact:Low
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Likelihood:High
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Covered Languages:Java
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Remediation Function:Constant/Issue
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Constant Cost:15min
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Analysis Scope:Main Sources
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Implementation details:
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FindBugs:HE_USE_OF_UNHASHABLE_CLASS, HE_SIGNATURE_DECLARES_HASHING_OF_UNHASHABLE_CLASS
Description
Because Object implements hashCode, any Java class can be put into a hash structure. However, classes that define equals(Object) but not hashCode() aren't truly hash-able because instances that are equivalent according to the equals method can return different hashes.
Noncompliant Code Example
public class Student { // no hashCode() method; not hash-able // ... public boolean equals(Object o) { // ... } } public class School { private Map<Student, Integer> studentBody = // okay so far new HashTable<Student, Integer>(); // Noncompliant // ...
Compliant Solution
public class Student { // has hashCode() method; hash-able // ... public boolean equals(Object o) { // ... } public int hashCode() { // ... } } public class School { private Map<Student, Integer> studentBody = new HashTable<Student, Integer>(); // ...
Attachments
Issue Links
- is implemented by
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SONARJAVA-1600 Rule S2141: Classes that don't define "hashCode()" should not be used in hashes
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- Closed
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- is related to
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SONARJAVA-3449 FP on S2141 when equals() without default implementation is defined in an interface
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- Closed
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