== vs. .equals()

For all reference types, including Integer etc., the meaning of == and != is equality of pointer values, i.e. same data address in memory.

Rule: To test equality of the contents or value of a reference type, always use .equals().

Rule: To compare against null, use == or != .

Rule: To make an Integer from an int, either use:

• Integer myInteger = (Integer) myint;
  (casting)

• Integer myInteger = myint;
  (auto-boxing)

• Integer myInteger = Integer.valueOf(myint)

These can save storage:

• new Integer() always makes a new box, costing 16 bytes and (eventually) garbage collection.

• Integer.valueOf() will reuse a value in the Integer cache if possible, costing 0 bytes.