Review Question
4. What is message protocol?
Message protocol is the entire collection of methods of an object.
5. What is an overriding method?
Overriding method is method that overrides the inherited method.
7. What is dynamic dispatch?
Dynamic dispatch is the third characteristic (after abstract data types and inheritance) of object-oriented programming language which is a kind of polymorhphism provided by the dynamic binding of messages to method definitions.
10. What is an inner class?
Inner classes are non-static classes that are nested directly in another class.
11. What is the message protocol of an object?
The message protocol of an objects are all the methods.
12. From where are Smalltalk objects allocated?
Smalltalk objects are allocated from the heap and are referenced through reference variables, which are implicitly dereferenced.
15. What kind of inheritance, single or multiple, does Smalltalk support?
Smalltalk supports single inheritance; it does not allow multiple inheritance.
18. From where can C++ objects be allocated?
The objects of C++ can be static, stack dynamic, or heap dynamic. Explicit deallocation using the delete operator is required for heap-dynamic objects, because C++ does not include implicit storage reclamation.
19. How are C++ heap-allocated objects deallocated?
C++ heap-allocated objects are deallocated using destructor.
29. Does Objective-C support multiple inheritance?
No Objective-C doesn’t support it. (It supports only single inheritance).
31. What is the root class in Objective-C?
The predefined root class named NSObject
38. What is boxing?
Boxing is primitive values in Java 5.0+ which is implicitly coerced when they are put in object context. This coercion converts the primitive value to an object of the wrapper class of the primitive value’s type.
39. How are Java objects deallocated?
By implicitly calling a finalize method when the garbage collector is about to reclaim the storage occupied by the object.
Problem Set
1 . What important part of support for inheritance is missing in Java?
Java does not support the private and protected derivations of C++. One can surmise that the Java designers believed that subclasses should be subtypes, which they are not when private and protected derivations are supported. Thus, they did not include them.
7. What is one programming situation where multiple inheritance has a significant disadvantage over interfaces?
A situation when there are two classes derived from a common parent and those two derived class has one child.
10. Explain one advantage of inheritance.
Inheritance offers a solution to both the modification problem posed by abstract data type reuse and the program organization problem. If a new abstract data type can inherit the data and functionality of some existing type, and is also allowed to modify some of those entities and add new entities, reuse and is also allowed to modify some of those entities and add new entities, reuse is greatly facilitated without requiring change to the reused abstract data type. Programmers can begin with an existing abstract data type and design a modified descendant of it to fit a new problem requirement. Furthermore, inheritance provides a framework for the definition of hierarchies of related classes that can reflect the descendant relationship in the problem space.
Message protocol is the entire collection of methods of an object.
5. What is an overriding method?
Overriding method is method that overrides the inherited method.
7. What is dynamic dispatch?
Dynamic dispatch is the third characteristic (after abstract data types and inheritance) of object-oriented programming language which is a kind of polymorhphism provided by the dynamic binding of messages to method definitions.
10. What is an inner class?
Inner classes are non-static classes that are nested directly in another class.
11. What is the message protocol of an object?
The message protocol of an objects are all the methods.
12. From where are Smalltalk objects allocated?
Smalltalk objects are allocated from the heap and are referenced through reference variables, which are implicitly dereferenced.
15. What kind of inheritance, single or multiple, does Smalltalk support?
Smalltalk supports single inheritance; it does not allow multiple inheritance.
18. From where can C++ objects be allocated?
The objects of C++ can be static, stack dynamic, or heap dynamic. Explicit deallocation using the delete operator is required for heap-dynamic objects, because C++ does not include implicit storage reclamation.
19. How are C++ heap-allocated objects deallocated?
C++ heap-allocated objects are deallocated using destructor.
29. Does Objective-C support multiple inheritance?
No Objective-C doesn’t support it. (It supports only single inheritance).
31. What is the root class in Objective-C?
The predefined root class named NSObject
38. What is boxing?
Boxing is primitive values in Java 5.0+ which is implicitly coerced when they are put in object context. This coercion converts the primitive value to an object of the wrapper class of the primitive value’s type.
39. How are Java objects deallocated?
By implicitly calling a finalize method when the garbage collector is about to reclaim the storage occupied by the object.
Problem Set
1 . What important part of support for inheritance is missing in Java?
Java does not support the private and protected derivations of C++. One can surmise that the Java designers believed that subclasses should be subtypes, which they are not when private and protected derivations are supported. Thus, they did not include them.
7. What is one programming situation where multiple inheritance has a significant disadvantage over interfaces?
A situation when there are two classes derived from a common parent and those two derived class has one child.
10. Explain one advantage of inheritance.
Inheritance offers a solution to both the modification problem posed by abstract data type reuse and the program organization problem. If a new abstract data type can inherit the data and functionality of some existing type, and is also allowed to modify some of those entities and add new entities, reuse and is also allowed to modify some of those entities and add new entities, reuse is greatly facilitated without requiring change to the reused abstract data type. Programmers can begin with an existing abstract data type and design a modified descendant of it to fit a new problem requirement. Furthermore, inheritance provides a framework for the definition of hierarchies of related classes that can reflect the descendant relationship in the problem space.
12. Compare inheritance and nested classes in C++. Which of these supports an is-a relationship?
Inheritance is where one class (child class) inherits the members of another class (parent class).Nested class is a class declared entirely within the body of another class or interface. Meanwhile, Inheritance does support it.
Inheritance is where one class (child class) inherits the members of another class (parent class).Nested class is a class declared entirely within the body of another class or interface. Meanwhile, Inheritance does support it.
13. Describe the mechanism of dynamic dispatch with an example in Java. Is it possible to dynamically dispatch the data members?
In C++, a method must be defined as virtual to allow dynamic binding. In Java, all method calls are dynamically bound unless the called method has been defined as final, in which case it cannot be overridden and all bindings are static. Static binding is also used if the method is static or private, both of which disallow overriding.
17. What are the different options for object destruction in Java?
There is no explicit deallocation operator. A finalize method is implicitly called when the garbage collector is about to reclaim the storage occupied by the object.
In C++, the programmer can specify whether static binding or dynamic binding is to be used. Because static binding is faster, this is an advantage for those situations where dynamic binding is not necessary. Furthermore, even the dynamic binding in C++ is fast when compared with that of Smalltalk. Binding a virtual member function call in C++ to a function definition has a fixed cost, regardless of how distant in the inheritance hierarchy the definition appears. Calls to virtual functions require only five more memory references than statically bound calls (Stroustrup, 1988). In Smalltalk, however, messages are always dynamically bound to methods, and the farther away in the inheritance hierarchy the correct method is, the longer it takes. The disadvantage of allowing the user to decide which bindings are static and which are dynamic is that the original design must include these decisions, which may have to be changed later.
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