Abstract Data Types and Encapsulation Constructs

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Abstract Data Types andEncapsulation Constructs

• Jianhua Yang
• Department of Math and Computer Science
• Bennett College

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Outline

• The concept of abstraction
• Introduction to data abstraction
• Design issues for abstraction data types
• Language examples
• Parameterized abstract data types
• Encapsulation constructs
• Naming encapsulations

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11.1 The concept of abstraction

• An abstraction is a view or representation of an
  entity that includes only the most significant
  attributes.
• It allows programmers to focus on essential
  attributes, while ignoring subordinate
  attributes.
• Two abstractions data, process

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Purpose

• Its purpose is to simplify the programming process

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Process abstraction

• All subprograms are process abstractions

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Data abstraction

• What is it?

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11.2 Introduction to Data Abstraction

• An abstract data type is an enclosure that
  includes only the data representation of one
  specific data type and the subprograms that
  provide the operations for that type.

• An instance of an abstract data type is called an
  object.

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1. Floating-point as an Abstract Data Type

• float x, y, z

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2. User defined Abstract Data Types

• Should be the same as the language-defined types
• A type definition that allows program units to
  declare variables of the type but hides the
  representation of objects of the type
• A set of operations for manipulating objects of
  the type.

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An abstract data type

• Must satisfy the following two conditions
• The declarations of the types and the operations
  on the objects of the type are contained in a
  single syntactic unit.
• The representation of objects of the type is
  hidden from the program units that use the types.

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Advantages

• 1. It provides a method of organizing a program
  into logical units that can be compiled
  separately.
• 2. Keep specifications and implementation
  separate.
• 3. Increase reliability.
• 4. Easy to maintain.

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3. An Example

• An abstract data type stack
• Operations
• Create(stack)
• Destroy(stack)
• Empty(stack)
• Push(stack, element)
• Pop(stack)
• Top(stack)

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11.3 Design issues for ADT

• Encapsulation
• Information hiding

package class
Public Private Protected
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11.4 Language Examples

• ADT in Ada
• ADT in C
• ADT in Java
• ADT in C

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1. ADT in C

• Struct
• Class

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1) Class (Encapsulation)

• Data members
• Member functions

The data defined in a C class are called data
members
The functions defined in a class are called
member functions
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Data members

• Stack-dynamic
• Heap-dynamic

C provides the new and delete operators to
manage the heap.
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Member functions

• Can be defined in two distinct ways
• 1. complete definition can appear in the class
• 2. only its header is in the class.

inline
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2) Information hiding

• Private
• Public
• Protected

Information that is to be hidden is treated as
private attributes.
Information that is to be visible is treated as
public attributes.
Information that is to be between private and
public is treated as protected attributes.
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3) An Example
void main() int topOne stack
stk stk.push(42) stk.push(17) topOne
stk.top() stk.pop()

• class stack
• private
• int stackPtr
• int maxLen
• int topPtr
• public
• stack()
• stackPtr new int100
• maxLen99
• topPtr-1
• stack() delete stackPtr
• void push (int number)
• if (topPtrmaxLen)
• cerrltlterror in push-stack
• else
• stackPtrtopPtrnumber
• void pop()

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2. ADT in Java

• import java.io.
• class StackClass //beginning of StackClass
• private int stackRef
• private int maxLen, topIndex
• public StackClass() // A constructor
• stackRef new int 100
• maxLen 99
• topIndex -1

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ADT in Java (Cont.)

• public void push (int number)
• if (topIndex maxLen)
• System.out.println(Error- stack is full)
• else stackReftopIndex number
• public void pop()
• if(topIndex -1)
• System.out.println(Error stack is empty)
• else --topIndex

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ADT in Java (Cont.)

• public int top() return (stackReftopIndex)
• public boolean empty() return (topIndex
  -1)
• //end of StackClass

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An example to use StackClass

• public class TstStack
• public static void main(String args)
• StackClass myStack new StackCalss()
• myStack.push(42)
• myStack.push(29)
• System.out.println(29 is myStack.top())
• myStack.pop()
• System.out.println(42 is myStack.top())
• myStack.pop()
• myStack.pop() //Produces an error message

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3. ADT in C

• public class Weather
• public int DegreeDays
• get
• return degreeDays
• set
• degreeDays value
• prinvate int degreeDays

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ADT in C using this class

• Weather w new Weather()
• int degreeDaysToday, oldDegreeDays
• w.DegreeDays degreeDaysToday
• oldDegreeDays w.DegreeDays

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11.5 Parameterized ADT

• It is to design a stack abstract data type that
  can store any scalar type elements rather than
  being required to write a separate stack ADT for
  every different scalar type.

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An example with C

• include ltiostream.hgt
• template ltclass Typegt
• class stack //beginning of stack class
• private
• Type stackPtr
• int maxLen
• int topPtr
• public
• //A constructor for 100 element stacks
• stack()
• stackPtr new Type100
• maxLen 99
• topPtr -1

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An example with C (Cont.)

• stack() delete stackPtr
• void push(Type number)
• if(topPtr maxLen) coutltltError stack is
  fullltltendl
• else stackPtr topPtr number
• void pop()
• if(topPtr -1) cout ltltError- stack is
  emptyltltendl
• else topPtr --
• Type top() return (stackPtrtopPtr)
• int empty() return (topPtr -1)
• // end of stack class

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11.6 Naming Encapsulations

• for constructing a large program
• 1. work cooperation
• 2. using Library.

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Naming Encapsulations

• It define name scopes that assist in avoiding
  these name conflicts.

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1. C namespaces

• C includes a specification, namespace, that
  helps programs manage the problem of global
  namespaces.

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Example

• namespace MyStack
• // stack declarations
• Two ways
• 1. direct way MyStacktopPtr
• 2. indirct way
• using namespace MyStack
• p topPtr

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Summary

• Data abstraction
• Class
• Parameterized ADT
• Naming Encapsulations