OOP design

Question 1

Scanner

Answer 1

The scanner begins the analysis of the source
program by reading the input, character by
character, and grouping characters into
individual words and symbols (tokens)

Question 2

Parser

Answer 2

Given a formal syntax specification (typically
as a context-free grammar [CFG] ), the
parser reads tokens and groups them into
units as specified by the productions of the
CFG being used.
➢As syntactic structure is recognized, the
parser either calls corresponding semantic
routines directly or builds a syntax tree.

Question 3

Semantic Routines

Answer 3

Perform two functions
◼ Check the static semantics of each
construct
◼ Do the actual translation
◼ Intermediate representation is the representation
of the program in a language internal to the compiler

Question 4

Optimizer

Answer 4

The IR code generated by the semantic routines is
analyzed and transformed into functionally equivalent
but improved IR code
This phase can be very complex and slow
->loop optimization, register allocation, code scheduling

Question 5

Code Generator

Answer 5

➢Interpretive Code Generation
➢Grammar-Based Code Generator

Question 6

Primitive vs Non-primitive (Object)

Answer 6

• Primitive types are predefined in Java.
• Non-primitive types are created by the programmer
  and is not defined by Java (except for String).
• Non-primitive types can be used to call methods to
  perform certain operations, while primitive types
  cannot.
• A primitive type has always a value, while non-
  primitive types can be null.

Question 7

A collection is a unit

Answer 7

that contains a group of objects, e.g.,
a list of students …
* Java defines a collections framework since JDK 1.2,
which is a unified architecture for representing and
manipulating collections, allowing them to be
manipulated independent of the details of their
representation.
* Java collections framework contains:
* Interfaces
* Implementations
* Algorithms

Question 8

Benefits of Java Collections Framework

Answer 8

• Reduced Development Effort – It comes with
  almost all common types of collections and
  useful methods to iterate and manipulate the
  data.
• Increased Quality – Using core collection
  classes that are well tested increases our
  program quality rather than using any home
  developed data structure.
• Reusability and Interoperability

Question 9

public interface Iterable<T></T>

Answer 9

• T - the type of elements returned by the iterator
• Implementing this interface allows an object to be the
  target of the “for-each loop” statement, i.e., allows it
  to be iterated

Question 10

Iterators

Answer 10

An Iterator is an object that enables you to traverse
through a collection and to remove elements from the
collection selectively, if desired. You get an Iterator for
a collection by calling its iterator() method. The
following is the Iterator interface.

Question 11

Overriding (via inheritance)

Answer 11

Replacing an inherited method with another having the same signature

Question 12

Overloading

Answer 12

Two or more methods with different signatures

Question 13

Inheritance is transitive

Answer 13

An instance of class Parrot is also an instance of Bird, an instance
of Animal, …, and an instance of class Object

Question 14

Overriding by Replacement

Answer 14

Defining Methods in the Child Class:
Overriding by Replacement
* A child class can override the definition of an inherited method in
favor of its own
* that is, a child can redefine a method that it inherits from its parent
* the new method must have the same signature as the parent’s method,
but can have different code in the body
* In java, all methods except of constructors override the methods of
their ancestor class by replacement. E.g.:
* the Animal class has method eat()
* the Bird class has method eat() and Bird extends Animal
* variable b is of class Bird, i.e. Bird b = …
* b.eat() simply invokes the eat() method of the Bird class
* If a method is declared with the final modifier, it cannot be
overridden

Question 15

Overloading vs. Overriding

Answer 15

• Overloading deals with
  multiple methods in the
  same class with the same
  name but different
  signatures
• Overloading lets you
  define a similar operation
  in different ways for
  different data
• Overriding deals with two
  methods, one in a parent
  class and one in a child
  class, that have the same
  signature
• Overriding lets you define
  a similar operation in
  different ways for
  different object types

Question 16

Multiple Inheritance

Answer 16

• “diamond problem”, where it may be ambiguous
  as to which parent class a particular feature is
  inherited from if more than one parent class
  implements the same feature.
• Java doesn’t support Multiple Inheritance, i.e.,
  can not extends more than one superclass
• C++, Perl, Python support multiple inheritance

Question 17

Superclasses are created through the process called
“generalization”

Answer 17

What is an Abstract class?
Superclasses are created through the process called
“generalization”
Common features (methods or variables) are factored out of object
classifications (ie. classes).
Those features are formalized in a class, i.e., superclass
The classes from which the common features were taken become
subclasses to the newly created super class
Superclass does not have a “meaning” or does not directly
relate to a “thing” in the real world
It is an artifact of the generalization process
Because of this, abstract classes cannot be instantiated
They act as place holders for abstraction
Abstract classes are used heavily in Design Patterns
Creational Patterns: Abstract class provides interface for creating
objects. The subclasses do the actual object creation.
Structural Patterns: How objects are structured is handled by an abstract
class. What the objects do is handled by the subclasses.
Behavioural Patterns: Behavioural interface is declared in an abstract
superclass. Implementation of the interface is provided by subclasses.
In general: When one needs to generalize (abstract, factor out) common
properties and/or behaviours of conceptually related classes
Be careful not to overuse abstract classes
Every abstract class increases the complexity of your design
Every subclass increases the complexity of your design
Ensure that you receive acceptable return in terms of functionality given
the added complexity.

Question 18

Abstract Methods

Answer 18

Methods can also be abstracted
An abstract method is one to which a signature has been provided, but no
implementation for that method is given.
An Abstract method is a placeholder. It means that we declare that a
method must exist, but there is no meaningful implementation for that
methods within this class
Any class which contains an abstract method MUST also be
abstract
Any class which has an incomplete method definition cannot be
instantiated (i.e., it is abstract)
Abstract classes can contain both concrete and abstract
methods.
If a method can be implemented within an abstract class, and
implementation should be provided.

Question 19

What is an Interface?

Answer 19

An interface is similar to an abstract class with the following
exceptions:
All methods defined in an interface are abstract. Interfaces can contain no
implementation.
Interfaces cannot contain instance variables. However, they can contain
public static final variables (ie. constant class variables)
*Note: this is changing in the latest versions of Java. In this course, we maintain the
traditional definition of the interface.
Interfaces are declared using the “interface” keyword
If an interface is public, it must be contained in a file which has
the same name.
Interfaces are more abstract than abstract classes. There is no
hierarchy among them. Interfaces can extend other interfaces.
This creates a parent-child hierarchy.
Interfaces are implemented by classes using the “implements”
keyword.
A Class can only extends from one superclass. However, a
class may implement several Interfaces
The interfaces that a class implements are separated by commas
Any class which implements an interface must provide an
implementation for all methods defined within the
interface.
NOTE: if an abstract class implements an interface, it NEED NOT
implement all methods defined in the interface. HOWEVER, each
concrete subclass MUST implement the methods defined in the
interface.
An interface can extend multiple interfaces
Interfaces can inherit method signatures from other interfaces

Question 20

Abstract Classes Versus Interfaces

Answer 20

Abstract Classes Versus Interfaces
When should one use an Abstract class instead of an
interface?
If the subclass-superclass relationship is genuinely an “is a”
relationship.
If the abstract class can provide an implementation at the
appropriate level of abstraction
When should one use an interface in place of an
Abstract Class?
When the level of abstraction of the methods is such that they
can be used by a huge variety of other abstractions
When the subclass needs to inherit from another class
When you cannot reasonably implement any of the methods