Chapter 11

Concept of Programming Languages by Robert W. Sebesta Answer

Review Questions

1. What are the two kinds of abstractions in programming       languages ?

Process Abstraction and Data Abstraction

2. Define abstract data type

A data structure in the form of a record, but which includes subprograms that manipulate its data.

3. What are the advantages of the two parts of the definition of abstract data type ?

Increased reliability, Reduces range of code and number of variables which a programmer must be aware when writing / reading part of program. Make name conflict less likely to happen

5. What are the language design issues for abstract data types ?

ADTs must have a function that allows a user to modify a value inside that data type. Although the method is public, the value itself must be private.

10. What is the use of the Ada with clause ?

To make the names defined in external packages visible

11. What is the use of the Ada use clause ?

To eliminate the need for explicit qualification of the references to entities from the named package.

12. What is the fundamental difference between a C++ class and an Ada package ?

Class must be accessed from an instance of itself while package can be accessed directly.

13. From where are C++ objects allocated ?

From heap

15. What is the purpose of a C++ destructor ?

To deallocate heap space the object used.

16. What are the legal return types of a destructor ?

destructor has no return type

Problem Set

2. Suppose someone designed a stack abstract data type in which the function top returned an access path (or pointer ) rather than returning a copy of the top element. This is not a true data abstraction. Why ? Give an example that illustrates the problem.

The problem with this is that the user is given access to the stack through the returned value of the “top” function. For example, if p is a pointer to objects of the type stored in the stack, we could have:

p = top(stack1);

*p = 42;

These statements access the stack directly, which violates the principle of a data abstraction.

4. What are the advantages of the nonpointer concept in Java ?

- Variable Access are absolutely defined by the programmer

- No memory leak (i.e. dangling pointers, nameless variables etc)

9. What happens if the constructor is absent in Java and C++ ?

The compiler will automatically make a default one

11. Why is the destructor of C# rarely used ?

Because C# has its own garbage collection method , just like Java