2. Why is Java not a pure object oriented language? Java supports primitive data types - byte, boolean, char, short, int, float, long, and double and hence it is not a pure object oriented language. 3. Difference between Heap and Stack Memory in java. And how java utilizes this. Stack memory is the portion of memory that was assigned to every individual program. And it was fixed. On the other hand, Heap memory is the portion that was not allocated to the java program but it will be available for use by the java program when it is required, mostly during the runtime of the program.