Common case for comparing two objects references

Question

Beside checking if null (something == null) when do we use object reference comparisons in Java?

I can't think of any case to use object reference comparisons. For me that seems a little weird for a language abstracting all memory allocations.

Answer 1

1. Comparing singletons - singleton should has only one instance and could be checked for identity instead of equality.
2. Comparing enums (enums are singletons)

3. In some equals methods themselves like in (AbstractList):

   public boolean equals(Object o) {
       // Checking identity here you can avoid further comparison and improve performance.
       if (o == this)
           return true;
       if (!(o instanceof List))
           return false;
   
       ListIterator<E> e1 = listIterator();
       ListIterator<?> e2 = ((List<?>) o).listIterator();
       while (e1.hasNext() && e2.hasNext()) {
           E o1 = e1.next();
           Object o2 = e2.next();
           if (!(o1==null ? o2==null : o1.equals(o2)))
               return false;
       }
       return !(e1.hasNext() || e2.hasNext());
   }