65 lines
1.7 KiB
Plaintext
65 lines
1.7 KiB
Plaintext
Maps use hashes of the keys to select a bucket to store data in.
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Objects that hash to the same value will be added to the same bucket.
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When the hashing function has a poor distribution, buckets can grow to very large sizes.
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This may negatively affect lookup performance, as, by default, matching a key within a bucket has linear complexity.
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In addition, as the default hashCode function can be selected at runtime, performance expectations cannot be maintained.
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Implementing Comparable mitigates the performance issue for objects that hash to the same value.
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== Noncompliant Code Example
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[source,java]
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----
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class MyKeyType {
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// ...
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}
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class Program {
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Map<MyKeyType, MyValueType> data = new HashMap<>(); // Noncompliant
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Map<MyKeyType, MyValueType> buildMap() { // Noncompliant
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//...
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}
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}
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----
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== Compliant Solution
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[source,java]
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----
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class MyKeyType implements Comparable<MyKeyType> {
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// ...
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}
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class MyChildKeyType extends MyKeyType {
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// ...
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}
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class Program {
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Map<MyKeyType, MyValueType> data = new HashMap<>();
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Map<MyChildKeyType, MyValueType> data = new HashMap<>();
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Map<MyKeyType, MyValueType> buildMap() {
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//...
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}
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}
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----
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== See
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- https://www.kb.cert.org/vuls/id/903934
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- https://dzone.com/articles/java-8-hashmaps-keys-and-the-comparable-interface
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- https://github.com/openjdk/jdk/blob/4927ee426aedbeea0f4119bac0a342c6d3576762/src/hotspot/share/runtime/synchronizer.cpp#L760-L798
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- https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Comparable.html
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ifdef::env-github,rspecator-view[]
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=== Implementation Specification
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include::message.adoc[]
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include::highlighting.adoc[]
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endif::env-github,rspecator-view[]
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