encapsulation presentation

8/11/2019 Encapsulation Presentation

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Encapsulation


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Problem Defined

class Program

{

public class Account()

{

private float accountbalance=500;

------

------

-------so on

}

public static void main()

{

//If someone change the value of accountbalance here.

Account myaccount=new Account();

myaccount.accountbalance=500000;

float mybalance=myaccount.accountbalance;

print(mybalance);

// Here we will get the changed value instead of getting orignal value.

}

}


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Problem Solution

Solution to this problem is encapsulation.

Also known as information hiding.

It is basic feature of all the languages.

Help in creating section data type for programmers.

Section data types are those which are used byprogrammers without known its internal behavior.


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Different concepts for languages

A language mechanism for restricting access to someof object component.

A language construct facility bundling of data with

methods operating on data. In other words,wrapping up of data and functions into a single unit.


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Problem Solution for Example

class Program

{

public class Account()

{

private decimal accountbalance=500;

public decimal CheckBalance()

{return accountbalance;

}

}

public static void main()

{

Account myaccount=new Account();float mybalance=myaccount.CheckBalance();

}

}


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Various Mechanism

Four basic mechanism exist to provide programmerwith ability to create new data types and operationon the type:

1) Structured Data or Data Structures.

2) Sub Program.

3) Type Declaration.

4) Inheritance.


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1) Structured Data

Creating complex data objects out of elementarydata object defined by language designs.

A data structure is a data object that contain other

data object as its elements or components. Eg: Array, List and Record


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Specification of Data Structure Types

Number of components

May be fixed sized (Array and Record).

May be variable (Stack, tables and Link List).

Types of each components. Homogeneous (Array and files).

Non-homogeneous (Record).

Names to be used for selecting components

It is selection mechanism required to access components. Sayaccess mechanism.

Example : Array


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Operations on Data Structures

Component selection operation

Random Selection

Sequential Selection

Whole data structure operation Can take whole data structure as input and produce result in

form of similar type data structure. Example Addition of array.

Insertion and deletion of component.

Creation and destruction of data structure.


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Storage Representation

It includes:

Storage for component of data structure

An optional descriptor for storing attributes of data structure.

Methods: Sequentially.

Linked.

Sequential method used for fixed sized (Array).

Linked used for variable size (Linked List).


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Storage Representation


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Actual Implementation

For Sequential

One method is serial access(For Loop).

Second method is random access. For this, we need baseaddress and size of component to find the offset.

Offset = I * component size;

I location number to access.

Component size according to data type.


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Accessing components of array


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Actual Implementation Cont.

For linked

We need to know all the pointer values if we have to jump tosome point.

We must know the current position of the pointer and its

correspondence pointer value.


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Storage management in Data Structures

The life time of any data object begins when thebinding of object to particular location is made.

The lifetime end when the binding of object to

storage block is dissolved. For data structure of variable size, individual

components of the structure have their own lifetime,that is determined when they are inserted or get

deleted from the data structure.


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Storage management in Data Structures Cont.

Access path: At the time when data object is created,an access path to the data object must also be createdso that the data object can be accessed by operationsin the program.

After work has done access path is destroyed. It canbe destroyed in various ways: Assign a new value to the data object.

By return from subprogram into main program.


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Storage management problem issue

Two main problems in storage management arisebecause of data paths are:

Garbage: Even when access paths have been destroyed thedata object may exist in memory, these data objects are called

as garbage. As access paths have been destroyed, no programcan access data objects, there is wastage of memory.

Dangling references: A dangling reference is an access paththat continuous to exist after the lifetime of the associated data

object. After data object life is finished it restore the memoryfor further re-allocation, but it may not destroy the access pathleading to create dangling references. May help in breach datasecurity.


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Declarations and type checking for DS

Data structures are more complex, thus requiredmore information to specify while declaring them.

Data type

Number of dimensions.

Number of components.

Subscript naming.

Data type of each component.

Example: float A[20];

Array, one, 20, 0-19, float.


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Type checking

Existence of selected component: If we try to accessout of bound values that does not exist may lead toerror.

Type of selected component: A selection sequencemay define a complex path. Problems occurs whiletype checking.


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Vector and Array

A vector is a data structure composed of a fixednumber of components of same type organized as asimple linear structure.

A vector is one dimensional. An array is two dimensional. It has components

stored in rectangular grid of rows and columns. Wecan access any element using row and column

subscript.


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Vector attributes

Number of components.

Data type of each component.

Subscript to be used to access each component.

We already have discussed these.


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Operations on Vector

The operation that select a component from a vectoris called as subscripting.

It is usually written as vector name followed by

subscript of component to be selected. Example : V[2];

Other operations may include: Creation

Destroy Update

Assign one to other (Whole DS operations).


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Implementation


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Implementation Continues


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Multidimensional array

An array can be of two dimensional or threedimensional.

Syntax:datatype name [dimentiona 1][dimention 2];

Example:float hello[3][4];

Operations are same as vectors.


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Actual Implementation


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Slices

A slice is sub-structure of the an array that is array.

PL/I was the first language to implement slices.


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Records(Structure)

Fixed number of components with different data types.

Component of record can be heterogeneous.

Component of record are named with symbolic namesrather than subscript.

Example: struct EmployeeType

{ int ID;

int Age;

float Salary;

char Dept;

}Obj;


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Operations on Record

Various attributes to be declared in prior declaration: Number of components (4).

Data type of each component (int , float, char).

Selector used to name each component( ).

struct EmployeeType

{ int ID;int Age;

float Salary;

char Dept;

}Obj;

In this we access the elements using object i.e. Obj. Obj.Id;

Obj.Dept;


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Implemention

The storage representation is done using a singleblock.

The element with maximum storage is taken as base

to construct that block.


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Array of records

We can also use array of record as a data structure.

Example:

struct EmployeeType

{

int ID;int Age;

float Salary;

char Dept;

}Obj[500]; Here, we can store information of 500 employee.


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Multi-Level Record

Declaration Style:1 Employee,

2 Name,

3 Last CHARACTER (10),

3 Middle CHARACTER (15),

3 First CHARACTER (15),

2 Age FIXED(2),

2 Address,

3 Street

4 Number FIXED(5),4 St-Name CHARACTER(20),

3 City CHARACTER(15),

3 State CHARACTER(15),

3 Zip FIXED(5);


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Storage representation for record


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Variant Record

It provide us the facility to apply case on records.


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Lists

A data structure of an ordered sequence of datastructures is usually termed as List.

Specification:

Lists are rarely fixed length. Lists are rarely homogeneous.

Types: Stacks(Selection, Insertion and Deletion fixed to one end LIF))

Queues(Insertion and deletion on different ends). Trees

Directed Graph


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Sets

A set is a data object containing unordered collectionof distinct values.

Basic operations on set.

Membership: Is data X is member of set S.(X belongs to S). Insertion and deletion of single values: We can only insert the

data value X in set S if X is not already in set. Similarly, we canonly delete X if its member of S.

Union(Create new set of S1 and S2 with duplicate deleted).

Intersection( Have members both belongs to S1 And S2).

Difference of Sets(Set containing values in S1 but not in S2).


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