Introduction to OOP

Chapter 12: Implications of substitution:

Dynamic Memory Allocation

In the third approach, all objects are actually pointers.
Only enough space for a pointer is allocated at compile time.
Actual data storage is allocated on the heap at run-time.
Used in Smalltalk, Object Pascal, and Objective-C, Java.
Requires user to explicitly allocate new objects and, in some languages, explicitly free no longer used storage.
May also lead to pointer semantics for assignment and equality testing.