Key for indexing values of type T stored in a Context. ContextKey are compared by reference, so it is expected that only one ContextKey is created for a particular type of context value.

public class ContextUser {

  private static final ContextKey<MyState> KEY = ContextKey.named("MyState");

  public Context startWork() {
    return Context.withValues(KEY, new MyState());
  }

  public void continueWork(Context context) {
    MyState state = context.get(KEY);
    // Keys are compared by reference only.
    assert state != Context.current().get(ContextKey.named("MyState"));
    ...
  }
}