Your SlideShare is downloading. ×

Everything about Object Oriented Programming

1,370

Published on

Object Oriented Programming (OOP) makes it easier for programmers to structure and form software programs; since individual objects can be modified without touching other aspects of the …

Object Oriented Programming (OOP) makes it easier for programmers to structure and form software programs; since individual objects can be modified without touching other aspects of the program.

With this presentation we are covering most OOP features (Class, Object, Inheritance, Polymorphism, Encapsulation, etc.) with real life examples.

Published in: Education, Technology
0 Comments
8 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
1,370
On Slideshare
0
From Embeds
0
Number of Embeds
4
Actions
Shares
0
Downloads
114
Comments
0
Likes
8
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. • • • • https://www.facebook.com/Oxus20 oxus20@gmail.com Classes and Objects Encapsulation Inheritance Polymorphism Object Oriented Programming Abdul Rahman Sherzad
  • 2. Agenda » Object Oriented Programming » Definition and Demo ˃ Class ˃ Object ˃ Encapsulation (Information Hiding) ˃ Inheritance ˃ Polymorphism ˃ The instanceof Operator 2 https://www.facebook.com/Oxus20
  • 3. Object Oriented Programming (OOP) » OOP makes it easier for programmers to structure and form software programs. » For the reason that individual objects can be modified without touching other aspects of the program. ˃ It is also easier to update and modify programs written in object-oriented languages. » As software programs have grown larger over the years, OOP has made developing these large programs more manageable. 3 https://www.facebook.com/Oxus20
  • 4. Class Definition » A class is kind of a blueprint or template that refer to the methods and attributes that will be in each object. » BankAccount is a blueprint as follow ˃ State / Attributes + Name + Account number + Type of account + Balance ˃ Behaviors / Methods + To assign initial value + To deposit an account + To withdraw an account + To display name, account number & balance. Now you, me and others can have bank accounts (objects / instances) under the above BankAccount blueprint where each can have different account name, number and balance as well as I can deposit 500USD, you can deposit 300USD, as well as withdraw, etc. https://www.facebook.com/Oxus20 4
  • 5. BankAccount Class Example public class BankAccount { // BankAccount attributes private String accountNumber; private String accountName; private double balance; // BankAccount methods // the constructor public BankAccount(String accNumber, String accName) { accountNumber = accNumber; accountName = accName; balance = 0; } 5 https://www.facebook.com/Oxus20
  • 6. BankAccount Class Example (contd.) // methods to read the attributes public String getAccountName() { return accountName; } public String getAccountNumber() { return accountNumber; } public double getBalance() { return balance; } 6 https://www.facebook.com/Oxus20
  • 7. BankAccount Class Example (contd.) // methods to deposit and withdraw money public boolean deposit(double amount) { if (amount > 0) { balance = balance + amount; return true; } else { return false; } } public boolean withdraw(double amount) { if (amount > balance) { return false; } else { balance = balance - amount; return true; } } 7 } https://www.facebook.com/Oxus20
  • 8. Object Definition » An object holds both variables and methods; one object might represent you, a second object might represent me. » Consider the class of Man and Woman ˃ Me and You are objects » An Object is a particular instance of a given class. When you open a bank account; an object or instance of the class BankAccount will be created for you. https://www.facebook.com/Oxus20 8
  • 9. BankAccount Object Example BankAccount absherzad = new BankAccount("20120", "Abdul Rahman Sherzad"); » absherzad is an object of BankAccount with Account Number of "20120" and Account Name of "Abdul Rahman Sherzad". » absherzad object can deposit, withdraw as well as check the balance. 9 https://www.facebook.com/Oxus20
  • 10. BankAccount Demo public class BankAccountDemo { public static void main(String[] args) { BankAccount absherzad = new BankAccount("20120", "Abdul Rahman Sherzad"); absherzad.deposit(500); absherzad.deposit(1500); System.out.println("Balance is: " + absherzad.getBalance()); //2000 absherzad.withdraw(400); System.out.println("Balance is: " + absherzad.getBalance()); //1600 } } 10 https://www.facebook.com/Oxus20
  • 11. Encapsulation Definition » Encapsulation is the technique of making the class attributes private and providing access to the attributes via public methods. » If attributes are declared private, it cannot be accessed by anyone outside the class. ˃ For this reason, encapsulation is also referred to as Data Hiding (Information Hiding). » Encapsulation can be described as a protective barrier that prevents the code and data corruption. » The main benefit of encapsulation is the ability to modify our implemented code without breaking the code of others who use our code. https://www.facebook.com/Oxus20 11
  • 12. Encapsulation Benefit Demo public class EncapsulationDemo { public static void main(String[] args) { BankAccount absherzad = new BankAccount("20120", absherzad.deposit(500); "Abdul Rahman Sherzad"); // Not possible because withdraw() check the withdraw amount with balance // Because current balance is 500 and less than withdraw amount is 1000 absherzad.withdraw(1000); // Encapsulation Benefit // Not possible because class balance is private // and not accessible directly outside the BankAccount class absherzad.balance = 120000; // Encapsulation Benefit } } 12 https://www.facebook.com/Oxus20
  • 13. Inheritance Definition » inheritance is a mechanism for enhancing existing classes ˃ Inheritance is one of the other most powerful techniques of object-oriented programming ˃ Inheritance allows for large-scale code reuse » with inheritance, you can derive a new class from an existing one ˃ automatically inherit all of the attributes and methods of the existing class ˃ only need to add attributes and / or methods for new functionality 13 https://www.facebook.com/Oxus20
  • 14. BankAccount Inheritance Example » Savings Account is a bank account with interest » Checking Account is a bank account with transaction fees 14 https://www.facebook.com/Oxus20
  • 15. Specialty Bank Accounts » now we want to implement SavingsAccount and CheckingAccount ˃ A SavingsAccount is a bank account with an associated interest rate, interest is calculated and added to the balance periodically ˃ could copy-and-paste the code for BankAccount, then add an attribute for interest rate and a method for adding interest ˃ A CheckingAccount is a bank account with some number of free transactions, with a fee charged for subsequent transactions ˃ could copy-and-paste the code for BankAccount, then add an attribute to keep track of the number of transactions and a method for deducting fees 15 https://www.facebook.com/Oxus20
  • 16. Disadvantages of the copy-and-paste Approach » tedious and boring work » lots of duplicate and redundant code ˃ if you change the code in one place, you have to change it everywhere or else lose consistency (e.g., add customer name to the bank account info) » limits polymorphism (will explain later) 16 https://www.facebook.com/Oxus20
  • 17. SavingsAccount class (inheritance provides a better solution) » SavingsAccount can be defined to be a special kind of BankAccount » Automatically inherit common features (balance, account #, account name, deposit, withdraw) » Simply add the new features specific to a SavingsAccount » Need to store interest rate, provide method for adding interest to the balance » General form for inheritance: public class DERIVED_CLASS extends EXISTING_CLASS { ADDITIONAL_ATTRIBUTES ADDITIONAL_METHODS } 17 https://www.facebook.com/Oxus20
  • 18. SavingsAccount Class public class SavingsAccount extends BankAccount { private double interestRate; public SavingsAccount(String accNumber, String accName, double rate) { super(accNumber, accName); interestRate = rate; } public void addInterest() { double interest = getBalance() * interestRate / 100; this.deposit(interest); } } 18 https://www.facebook.com/Oxus20
  • 19. SavingsAccount Demo public class SavingsAccountDemo { public static void main(String[] args) { SavingsAccount saving = new SavingsAccount("20120", "Abdul Rahman Sherzad", 10); // deposit() is inherited from BankAccount (PARENT CLASS) saving.deposit(500); // getBalance() is also inherited from BankAccount (PARENT CLASS) System.out.println("Before Interest: " + saving.getBalance()); saving.addInterest(); System.out.println("After Interest: " + saving.getBalance()); } } 19 https://www.facebook.com/Oxus20
  • 20. CheckingAccount Class public class CheckingAccount extends BankAccount { private int transactionCount; private static final int NUM_FREE = 3; private static final double TRANS_FEE = 2.0; public CheckingAccount(String accNumber, String accName) { super(accNumber, accName); transactionCount = 0; } public boolean deposit(double amount) { if (super.deposit(amount)) { transactionCount++; return true; } return false; } 20 https://www.facebook.com/Oxus20
  • 21. CheckingAccount Class (contd.) public boolean withdraw(double amount) { if (super.withdraw(amount)) { transactionCount++; return true; } return false; } public void deductFees() { if (transactionCount > NUM_FREE) { double fees = TRANS_FEE * (transactionCount - NUM_FREE); if (super.withdraw(fees)) { transactionCount = 0; } } } } https://www.facebook.com/Oxus20 21
  • 22. CheckingAccount Demo public class CheckingAccountDemo { public static void main(String[] args) { CheckingAccount checking = new CheckingAccount("20120", "Abdul Rahman Sherzad"); checking.deposit(500); checking.withdraw(200); checking.deposit(700); // No deduction fee because we had only 3 transactions checking.deductFees(); System.out.println("transactions <= 3: " + checking.getBalance()); // One more transaction checking.deposit(200); // Deduction fee occurs because we have had 4 transactions checking.deductFees(); System.out.println("transactions > 3: " + checking.getBalance()); } 22 } https://www.facebook.com/Oxus20
  • 23. Polymorphism Definition » Polymorphism is the ability of an object to take on many forms. » The most common use of polymorphism in OOP occurs when a parent class reference is used to refer to a child class object. 23 https://www.facebook.com/Oxus20
  • 24. Polymorphism In BankAccount » A SavingsAccount IS_A BankAccount (with some extra functionality) » A CheckingAccount IS_A BankAccount (with some extra functionality) » Whatever you can do to a BankAccount (i.e. deposit, withdraw); you can do with a SavingsAccount or CheckingAccount » Derived classes can certainly do more (i.e. addInterest) for SavingsAccount) » Derived classes may do things differently (i.e. deposit for CheckingAccount) 24 https://www.facebook.com/Oxus20
  • 25. Polymorphism In BankAccount Example public class BankAccountPolymorphismDemo { public static void main(String[] args) { BankAccount firstAccount = new SavingsAccount("20120", "Abdul Rahman Sherzad", 10); BankAccount secondAccount = new CheckingAccount("20120", "Abdul Rahman Sherzad"); // calls the method defined in BankAccount firstAccount.deposit(100.0); // calls the method defined in CheckingAccount // because deposit() is overridden in CheckingAccount secondAccount.deposit(100.0); } } 25 https://www.facebook.com/Oxus20
  • 26. Instanceof Operator » if you need to determine the specific type of an object ˃ use the instanceof operator ˃ can then downcast from the general to the more specific type ˃ For example the object from BankAccount Parent Class will be casted to either SavingsAccount and/or CheckingAccount 26 https://www.facebook.com/Oxus20
  • 27. END 27 https://www.facebook.com/Oxus20

×