Object Oriented Programming

Chapter 2: Array of objects

Prepared by: Mahmoud Rafeek Alfarra

2016

Outlines◉User defined type

◉Array of User defined type (new class)

◉Passing Objects to Methods

◉Immutable Objects and Classes

◉Full Example

Note: I have prepared this material Based on (Liang: “Introduction to Programming using Java”, 10’th edition, 2015)

Lecture Let’s think on fieldes of class

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o As the defined class is a new data type, we can defined any variables or arrays of it.

User defined type

Array of User defined type

int sal;int id;String name;…

Employee classe1

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Employee [ ] x ;

Array of User defined type

o An array of objects is actually an array of reference variables.

Circle[] circleArray = new Circle[10];

Array of User defined type

Class [ ] x ;

Add objectsDelete objectsLooking for objectsPrinting all data….

ClassTo management many

objects which are stored in array

o Passing by value for primitive type value (the value is passed to the parameter)

o Passing by value for reference type value (the value is the reference to the object)

Passing Objects to Methods

Passing Objects to Methods

o For a class to be immutable, it must mark all data fields private and provide no mutator methods and no accessor methods that would return a reference to a mutable data field object.

o If the contents of an object cannot be changed once the object is created, the object is called an immutable object and its class is called an immutable class.

Immutable Objects and Classes

Immutable ? public class Student { private int id; private BirthDate birthDate;

public Student(int ssn, int year, int month, int day) { id = ssn; birthDate = new BirthDate(year, month, day); }

public int getId() { return id; }

public BirthDate getBirthDate() { return birthDate; }}

public class BirthDate { private int year; private int month; private int day; public BirthDate(int newYear, int newMonth, int newDay) { year = newYear; month = newMonth; day = newDay; } public void setYear(int newYear) { year = newYear; }}

Example: ContactBook

int serial;String name;String mobile;String address;…

Contact class

int count;void search(){}void print(){}void insert(){}…

ManagArray class

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Contact [ ] conArray ;

Objects of contact class

Manages the contacts

Contact bookclass Contact {

private String name; //….public Contact (String name, String mobile) { … }

}

class ManagArray {private Contact [ ] contBook; private int count;// …public ManagArray(int size){ … }public void insert(Contact c) { …. }

public void printData() { … }public void searchByName(String name) { … }

}

static int x;

class Test

obj1

X = 0X = 1

obj2

X = 2

obj3

X = 3

Now: Print Obj1.X

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Print Obj1.X

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Print Obj1.X

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Practices

Group 1Give 3 examples to array of objects.

Group 2Diffrenciate between Passing by value and by reference.

Group 3Develop Immutable class.

THANKS!

Any questions?You can find me at:

Fb/mahmoudRAlfarraStaff.cst.ps/mfarraYoutube.com/mralfarra1@mralfarra