69 lines
1.5 KiB
Plaintext
69 lines
1.5 KiB
Plaintext
The Java 8 version of ``++HashMap++`` handles key clashes by storing nodes in a binary tree when more than 11 keys clash with each other, and that tree needs to know the relative order of the keys. If you don't provide a ``++compareTo++`` method, ``++System.identityHashCode()++`` will be used as the fallback, and that typically returns a value based on the object's memory location, resulting in a performance degradation to ``++O(n)++`` where ``++n++`` is the number of objects at that map location.
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Therefore, it's considered a best practice to implement ``++compareTo++`` in classes that are used as ``++HashMap++`` keys.
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*Note* that this rule is automatically disabled when the project's ``++sonar.java.source++`` is lower than ``++8++``.
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== Noncompliant Code Example
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[source,java]
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----
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public class Key {
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@Override
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public boolean equals(Object obj) {
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/* ... */
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}
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@Override
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public int hashCode() {
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/* ... */
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}
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}
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public void doTheThing() {
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Map <Key,String> map = new HashMap<>(); // Noncompliant
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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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public class Key implements Comparable{
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@Override
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public boolean equals(Object obj) {
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/* ... */
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}
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@Override
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public int hashCode() {
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/* ... */
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}
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@Override
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public int compareTo(Object o) {
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//...
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}
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}
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public void doTheThing() {
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Map <Key,String> map = new HashMap<>();
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// ...
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}
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----
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ifdef::env-github,rspecator-view[]
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'''
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== Comments And Links
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(visible only on this page)
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include::comments-and-links.adoc[]
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endif::env-github,rspecator-view[]
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