InconsistentHashCode
Including fields in hashCode which are not compared in equals violates the contract of hashCode.

Severity
WARNING
Tags
FragileCode
Has Fix?
REQUIRES_HUMAN_ATTENTION

The problem

Implementations of Object#hashCode should not incorporate fields which the implementation of Object#equals does not. This violates the contract of hashCode: specifically, equal objects must have equal hashCodes.

```java {.bad} class Foo { private final int a; private final int b;

Foo(int a, int b) { this.a = a; this.b = b; }

@Override public boolean equals(@Nullable Object o) { return o instanceof Foo && ((Foo) o).a == a; }

@Override public int hashCode() { return a + 31 * b; } }

Foo first = new Foo(10, 20); Foo second = new Foo(10, 40);

first.equals(second) // true first.hashCode() == second.hashCode() // false ```

The fix for this class is either to include a comparison of b in the #equals method, or remove b from #hashCode. The former is more likely to be correct.

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("InconsistentHashCode") to the enclosing element.