Summary

Add java.util.Objects.newIdentity to supply a unique object with identity.
This is a replacement code can be used today for the traditional new Object() idiom, which will be deprecated under Project Valhalla.

Problem

Forward looking to JEP 401: Primitive Objects (Preview), the current practice using new Object() to create an object suitable for use as a unique key or synchronization is problematic.

Refer to [JEP 401: Primitive Classes (Preview)]https://openjdk.java.net/jeps/401

The naming and context are discussed on the valhalla-spec-experts emails Making Object Abstract.

Solution

Creating an API for the specific purpose of creating a unique object with identity enables a smooth transition away from the problematic use case and enables specific recommendations and transitional tools.

Specification

The method newIdentity() is added to java.util.Objects.

/**
 * {@return a new instance of an unspecified class}
 * The object has a unique identity; no other references to it exist.
 * It can be used for synchronization, or where a placeholder Object is needed.
 * The class does not override any of the methods of {@code java.lang.Object}.
 * Use this method to avoid relying on the {@linkplain Object#Object() Object constructor}.
 *
 * @since 17
 */
public static Object newIdentity() {...}

In java.lang.Object the javadoc in the constructor includes a link to java.util.Objects.newIdentity()

 /**
  * Constructs a new object.
  * @see Objects#newIdentity()
  */
 public Object() {}