'Comparable' implemented but 'equals()' not overridden

Reports classes that implement java.lang.Comparable but do not override equals().

If equals() is not overridden, the equals() implementation is not consistent with the compareTo() implementation. If an object of such a class is added to a collection such as java.util.SortedSet, this collection will violate the contract of java.util.Set, which is defined in terms of equals().

Example:

  class Length implements Comparable<Length> {
    private int cm = 0;

    @Override
    public int compareTo(@NotNull Length o) {
      if (cm == o.cm) return 0;
      return cm < o.cm ? -1 : 1;
    }
  }

After the quick fix is applied:

  class Length implements Comparable<Length> {
    private int cm = 0;

    @Override
    public int compareTo(@NotNull Length o) {
      if (cm == o.cm) return 0;
      return cm < o.cm ? -1 : 1;
    }

    @Override
    public boolean equals(Object o) {
      return o instanceof Length && compareTo((Length) o) == 0;
    }
  }

Locating this inspection

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ComparableImplementedButEqualsNotOverridden

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Availability

By default bundled with: IntelliJ IDEA 2024.1, Qodana for JVM 2024.1,
Can be installed with plugin: Java, 241.18072

Last modified: 18 June 2024