When implementing the
hashCode() method, we should ensure that it follows the general contract:
objects that are equal according to the
equals(Object) method must have the same hash code.
Additionally, it should be consistent (returning the same value during multiple invocations) and ideally distribute hash codes well to minimize collisions.
Important: When overriding
hashCode(), you must also override
equals() to maintain the general contract that equal objects must have equal hash codes.
The
hashCode() method is defined in the
java.lang.Object class. However, the default implementation does not necessarily return the object's internal address (this is implementation-dependent and may use identity hash codes):
public native int hashCode();
The
java.util.Objects class provides utility methods to safely get the hash code of an object or multiple objects:
public static int hashCode(Object o) {
return o != null ? o.hashCode() : 0;
}
public static int hash(Object... values) {
return Arrays.hashCode(values);
}
The
java.util.Arrays class provides utility methods to get the hash code of arrays,
including specific overloaded methods for each primitive type (e.g.,
hashCode(int[]),
hashCode(boolean[]), etc.).
It also provides
deepHashCode(Object[]) for computing hash codes of nested arrays.