CS 331, Principles of Programming Languages

1
CS 331, Principles of Programming Languages

• Chapter 7
• Object-Oriented Programming

2
What is an object?

• Represents some important entity in the
  application
• Has external and internal properties, which
  include some
• data, and
• operations to be applied to that data
• May be one of several similar objects

3
Terminology

• An object is an encapsulation of data and
  operations
• A class is a set of objects that have the same or
  similar properties (i.e. data and operations)
• A subclass is a subset of a class, with
  additional properties

4
More Terminology

• An individual object belonging to a given class
  is an instance of that class
• A method is a procedure body that implements an
  operation
• A message is a request to execute a method
• note that a message may or may not involve
  inter-process communication

5
Class Hierarchy?

• A subclass is derived from at least one parent
  class
• operations in the class can be applied to objects
  in any subclass, unless redefined
• Instances of subclass objects may have additional
  operations that can be applied
• Some OOPLs support multiple inheritance, where a
  class may have more than one parent

6
Classes and subclasses

• Tree
• node root(t tree)
• height(n node)
• n_of_immediate_descendants(n node)
• Binary tree
• left_child(n node) right_child(n node)
• Binary search tree
• tree insert(key K, value someDataType)

7
Another Parent Class?

• Class SearchableThing
• insert(K key, newDatasomeDataType)
• someDataType retrieve(K key)
• Boolean search(K key)
• cleanOut(K key)
• The Binary search tree class may have the same
  properties as Binary Tree and Searchable Thing