Objects.hashCode(Object o) should not be passed a primitive value


The problem

Objects.hashCode takes an Object parameter, and will either return 0 when the parameter is null, or call the underlying hashCode function of the Object reference.

Passing a primitive value to Objects.hashCode function results in boxing the primitive, then calling the boxed object’s hashCode. You can get the same result by using, e.g.: Long.hashCode(long) to get the effective hash code of a primitive long. If you’re calling this method outside of your own hashCode() implementation, prefer to use the BoxedClass.hashCode(primitive) functions to avoid unwanted boxed.

If you’re implementing a hashCode function for your own class that consists of a single primitive value, you may want to consider some of these alternatives:

public int hashCode() {
  // This function will box intValue into an Integer, and wrap *that* in an
  // array, but will generate a hashCode which is likely to be different than
  // the hashCode of the boxed version of the intValue. This makes it easier
  // to add more fields to the class and hashCode method (just by adding more
  // fields to the hash call), but comes at a potential performance penalty.
  return Objects.hash(intValue);
public int hashCode() {
  // This function will avoid boxing the int to an Integer, and is an explicit
  // acknowledgement that the hashCode() of *this* class is the same as the
  // hash code of the underlying intValue.
  return Integer.hashCode(intValue);


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