1 / 61

More OOP

More OOP. Lecturer :Royal University Of Phnom Penh Name :Chim Bunthoeurn Email : cbunthoeurn@yahoo.com Tel :012-899-304. Topics. Basic Concepts of OOP Inheritance Abstract class Interface Polymorphism Package. Basic Concepts of OO. An object has

harrison-mcintyre
Télécharger la présentation

More OOP

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. More OOP Lecturer :Royal University Of Phnom Penh Name :Chim Bunthoeurn Email :cbunthoeurn@yahoo.com Tel :012-899-304

  2. Topics • Basic Concepts of OOP • Inheritance • Abstract class • Interface • Polymorphism • Package Lecturer : chim bunthoeurn

  3. Basic Concepts of OO • An object has • state: defined by the set of fields or attributes. • behavior: defined by the set of methods or operation that can be applied to the object. • identity: determined at the creation time. • Class • A template for creating objects. • Objects of the same class exhibit the same behavior. They may have different states. Lecturer : chim bunthoeurn

  4. Objects and Classes In real world terms: • An object represents an individual entity or thing. • A class represents a group of objects that exhibit some common characteristics or behavior. • Classes are resulted from classification. • Examples of classes in real world: • Students, Graduate students • Undergraduate students • MS students • Ph.D. students Lecturer : chim bunthoeurn

  5. Objects and Classes In programming terms: • A class defines a self-contained software component that represents a real world class. • The design of classes should follows the basic principles of object-orientation: • modularity • encapsulation • Each object is an instance of its class. • A class defines the common characteristics of its instances: • the behaviors and • the templates of the fields. • Each object has its own state, i.e., the values of the fields. Lecturer : chim bunthoeurn

  6. Class Declaration • A class contains data (variable, field) declarations and method declarations • Variables declared at the class level can be used by all methods in that class • Variables declared within a method can only be used in that method • A method declaration specifies the code that will be executed when the method is invoked (or called) Lecturer : chim bunthoeurn

  7. Class Declaration Syntax [ ClassModifiers ] class ClassName  [ extends SuperClass ]  [ implements Interface1, Interface2  ...] {  ClassMemberDeclarations} Lecturer : chim bunthoeurn

  8. Class Visibility • publicAccessible everywhere. One public class allowed per file. The file must be named ClassName.java • default Accessible within the current package. • Other class modifiers: • abstractA class that contains abstract methods • finalNo subclasses Lecturer : chim bunthoeurn

  9. Field and Method Declaration [ MethodModifiers ] ResultType  Name ( [ ParameterList ]  ) {  Statements} [ FieldModifiers ] Type  FieldName1 [ = Initializer1 ] ,   FieldName2 [ = Initializer2 ] ...; Lecturer : chim bunthoeurn

  10. public protected package private The class itself Yes Yes Yes Yes Classes in the  same package  Yes Yes Yes No Subclasses in a  different package  Yes Yes No No Non-subclasses in  a different package Yes No No No Visibility Lecturer : chim bunthoeurn

  11. Relationship among Classes:Composition • Has-a relation • Example: a student has a • address (type: Address) • faculty advisor (type: Faculty) • etc. Lecturer : chim bunthoeurn

  12. Class Diagram: Composition Lecturer : chim bunthoeurn

  13. Relationship among Classes:Inheritance • A mechanism to organize classes by commonalities. • subclasses, specialization • superclass, generalization • Is-a relation • Example: • A graduate student is a student. • A Master student is a graduate student. • A Ph.D. student is a graduate student. • An undergraduate student is a student. Lecturer : chim bunthoeurn

  14. Class Diagram: Inheritance Lecturer : chim bunthoeurn

  15. Encapsulation • external view: for the users of the classs, client view • internal view: for the developers of the class, implementer view • visibility: • public, • protected, • package (default), • private Lecturer : chim bunthoeurn

  16. Example: Coin.java public class Coin { public final int HEADS = 0; public final int TAILS = 1; private int face; public Coin (){ flip(); } public void flip (){ face = (int) (Math.random() * 2); } Lecturer : chim bunthoeurn

  17. Example: Coin.java public int getFace () { return face; } public String toString() { String faceName; if (face == HEADS) faceName = "Heads"; else faceName = "Tails"; return faceName; } } Lecturer : chim bunthoeurn

  18. Example: CountFlips.java public class CountFlips { public static void main (String[] args) { final int NUM_FLIPS = 1000; int heads = 0, tails = 0; Coin myCoin = new Coin(); for (int count=1; count <= NUM_FLIPS; count++) { myCoin.flip(); if (myCoin.getFace() == myCoin.HEADS) heads++; else tails++; } System.out.println("The number flips: " + NUM_FLIPS); System.out.println("The number of heads: " + heads); System.out.println("The number of tails: " + tails); } } Lecturer : chim bunthoeurn

  19. Example: FlipRace:java public class FlipRace { public static void main (String[] args) { final int GOAL = 3; int count1 = 0, count2 = 0; // Create two separate coin objects Coin coin1 = new Coin(); Coin coin2 = new Coin(); while (count1 < GOAL && count2 < GOAL) { coin1.flip(); coin2.flip(); System.out.print ("Coin 1: " + coin1); System.out.println (" Coin 2: " + coin2); count1 = (coin1.getFace() == coin1.HEADS) ? count1+1 : 0; count2 = (coin2.getFace() == coin2.HEADS) ? count2+1 : 0; } Lecturer : chim bunthoeurn

  20. Example: FlipRace:java // Determine the winner if (count1 < GOAL) { System.out.println("Coin 2 Wins!"); } else if (count2 < GOAL) { System.out.println("Coin 1 Wins!"); } else { System.out.println("It's a TIE!"); } } } Lecturer : chim bunthoeurn

  21. Method Overloading • Two or more methods/constructors with the same name but different numbers or different types of parameters:void methodA(int i)void methodA(int i, int j) void methodB(int i)void methodB(float f) • Avoid overloading Lecturer : chim bunthoeurn

  22. Special Methods • public boolean equals(Object o) • o1.equals(o2)versuso1 == o2 • The equals() method tests the equality of two objects. • The == operator tests the identity of two objects. • When compare two strings, use s1.equals(s2) instead of s1 == s2. • public String toString() • returns a string representation of the state of the object Lecturer : chim bunthoeurn

  23. Example: Account.java import java.text.NumberFormat; public class Account { private NumberFormat fmt = NumberFormat.getCurrencyInstance(); private final double RATE = 0.045; // interest rate of 4.5% private long acctNumber; private double balance; private String name; public Account(String owner, long account, double initial) {name = owner; acctNumber = account; balance = initial; } Lecturer : chim bunthoeurn

  24. Example: Account.java public double deposit (double amount) { if (amount < 0) { // deposit value is negative System.out.println(); System.out.println("Error: ..."); System.out.println(acctNumber + " " + fmt.format(amount)); } else { balance = balance + amount; } return balance; } Lecturer : chim bunthoeurn

  25. Example: Account.java public double withdraw(double amount, double fee) { amount += fee; if (amount < 0) { // withdraw value is negative System.out.println ("Error: ..."); } else if (amount > balance) { // withdraw value exceeds balance System.out.println ("Error: ..."); } else { balance = balance - amount; } return balance; } Lecturer : chim bunthoeurn

  26. Example: Account.java public double addInterest () { balance += (balance * RATE); return balance; } public double getBalance () { return balance; } public long getAccountNumber () { return acctNumber; } public String toString () { return (acctNumber + "\t" + name + "\t" + fmt.format(balance)); } Lecturer : chim bunthoeurn

  27. Example: BankAccount.java public class BankAccounts { public static void main (String[] args) { Account acct1 = new Account("Ted Murphy", 72354, 102.56); Account acct2 = new Account("Jane Smith", 69713, 40.00); Account acct3 = new Account("Edward Demsey", 93757, 759.32); acct1.deposit (25.85); double smithBalance = acct2.deposit (500.00); System.out.println( "Smith balance after deposit: " + smithBalance); System.out.println( "Smith balance after withdrawal: " + acct2.withdraw (430.75, 1.50)); Lecturer : chim bunthoeurn

  28. Example: BankAccount.java acct3.withdraw (800.00, 0.0); // exceeds balance acct1.addInterest(); acct2.addInterest(); acct3.addInterest(); System.out.println(); System.out.println(acct1); System.out.println(acct2); System.out.println(acct3); } } Lecturer : chim bunthoeurn

  29. Inheritance • Inheritance allows a software developer to derive a new class from an existing one, for the purpose of reuse, enhancement, adaptation, etc. • superclass (a.k.a. base class) • subclass (a.k.a. derived class, extended class) • Inheritance models the is-a relationship. • If class E is an extended class of class B, then any object of E can act-as an object of B. Lecturer : chim bunthoeurn

  30. Example: Book.java class Book { protected int pages = 1500; public void pageMessage() { System.out.println("Number of pages: " + pages); } } Lecturer : chim bunthoeurn

  31. Example: Dictionary.java class Dictionary extends Book { private int definitions = 52500; public void definitionMessage() { System.out.println("Number of definitions: " + definitions); System.out.println("Definitions per page: " + definitions/pages); } } Lecturer : chim bunthoeurn

  32. Example: Words.java class Words { public static void main (String[] args) { Dictionary webster = new Dictionary(); webster.pageMessage(); webster.definitionMessage(); } } C:\Examples>java Words Number of pages: 1500 Number of definitions: 52500 Definitions per page: 35 Output: Lecturer : chim bunthoeurn

  33. Extending Classes • Protected visibility • Super constructor • Overriding • Super reference • Single vs. multiple inheritance • A class may have only one superclass Lecturer : chim bunthoeurn

  34. Example: Book2.java class Book2 { protected int pages; public Book2(int pages) { this.pages = pages; } public void pageMessage() { System.out.println("Number of pages: " + pages); } } Lecturer : chim bunthoeurn

  35. Example: Dictionary2.java class Dictionary2 extends Book2 { private int definitions; public Dictionary2(int pages, int definitions) { super (pages); this.definitions = definitions; } public void definitionMessage () { System.out.println("Number of definitions: " + definitions); System.out.println("Definitions per page: " + definitions/pages); } } Lecturer : chim bunthoeurn

  36. Example: Words2.java class Words2 { public static void main (String[] args) { Dictionary2 webster = new Dictionary2(1500, 52500); webster.pageMessage(); webster.definitionMessage(); } } Output: C:\Examples>java Words2 Number of pages: 1500 Number of definitions: 52500 Definitions per page: 35 Lecturer : chim bunthoeurn

  37. Example: Book3.java class Book3 { protected String title; protected int pages; public Book3(String title, int pages) { this.title = title; this.pages = pages; } public void info() { System.out.println("Title: " + title); System.out.println("Number of pages: " + pages); } } Lecturer : chim bunthoeurn

  38. Example: Dictionary3a.java class Dictionary3a extends Book3 { private int definitions; public Dictionary3a(String title, int pages, int definitions) { super (title, pages); this.definitions = definitions; } public void info() { System.out.println("Dictionary: " + title); System.out.println("Number of definitions: " + definitions); System.out.println("Definitions per page: " + definitions/pages); } } Lecturer : chim bunthoeurn

  39. Example: Dictionary3b.java class Dictionary3b extends Book3 { private int definitions; public Dictionary3b(String title, int pages, int definitions) { super (title, pages); this.definitions = definitions; } public void info() { super.info(); System.out.println("Number of definitions: " + definitions); System.out.println("Definitions per page: " + definitions/pages); } } Lecturer : chim bunthoeurn

  40. Example: Books.java class Books { public static void main (String[] args) { Book3 java = new Book3("Introduction to Java", 350); java.info(); System.out.println(); Dictionary3a webster1 = new Dictionary3a("Webster English Dictionary", 1500, 52500); webster1.info(); System.out.println(); Dictionary3b webster2 = new Dictionary3b("Webster English Dictionary", 1500, 52500); webster2.info(); } } Lecturer : chim bunthoeurn

  41. Example: Books.java Output: C:\Examples>java Books Title: Introduction to Java Number of pages: 350 Dictionary: Webster English Dictionary Number of definitions: 52500 Definitions per page: 35 Title: Webster English Dictionary Number of pages: 1500 Number of definitions: 52500 Definitions per page: 35 Lecturer : chim bunthoeurn

  42. Overloading vs. Overriding • Overloading • More than one methods have the same name but different signatures • Overriding • Replacing the implementation of a methods in the superclass with one of your own. • You can only override a method with the same signature. • You can only override instance methods. Lecturer : chim bunthoeurn

  43. The Object Class • The root of Java class hierarchy • Defines some common methods: • public String toString() • public boolean equals(Object other) • If a class does not explicitly declare a superclass, its superclass is Object. Lecturer : chim bunthoeurn

  44. Abstract Class • An abstract class is a class with partial implementation. • It implements behaviors that are common to all subclasses, but defers to the subclasses to implement others (abstract methods). • An abstract class cannot be instantiated • The subclass of an abstract class must override the abstract methods of the parent, or it too will be considered abstract Lecturer : chim bunthoeurn

  45. Interface • Interfaces are classes with no implementation. • Interfaces represent pure design. • Abstract classes represent mixed design and implementation. • An interface consists of only abstract methods and constants, i.e., static and final. • All methods and constants are public. • No static methods. • An interface cannot be instantiated Lecturer : chim bunthoeurn

  46. Inheritance on Interface • Inheritance relation also applies to interfaces • superinterface and subinterface • Multiple inheritance allowed • An interface may extend multiple interfaces • A class my implement multiple interfaces Lecturer : chim bunthoeurn

  47. Type ConversionImplicit Conversion • Numeric variables: Any numeric types can be converted to another numeric type with larger range, e.g. char ==> int, int ==> long, int ==> float, float ==> double. • Object reference: An object reference of class C can be converted to a reference of a superclass of C. Lecturer : chim bunthoeurn

  48. Type ConversionExplicit Conversion (Cast) • Numeric variables: Any numeric types can be explicitly cast to any other numeric type. May lose bits, precision. • Object reference: Cast an object reference of a class to a reference of any other class is: • syntactically allowed; but • runtime checked. Lecturer : chim bunthoeurn

  49. Cast Object References class Student { ... } class Undergraduate extends Student { ... } class Graduate extends Student { ... } Student student1, student2; student1 = new Undergraduate(); // ok student2 = new Graduate(); // ok Graduate student3; student3 = student2; // compilation error student3 = (Graduate) student2; // explicit cast, ok student3 = (Graduate) student1; // compilation ok, run-time error Lecturer : chim bunthoeurn

  50. Polymorphic Reference • A polymorphic reference is one which can refer to different types of objects. Lecturer : chim bunthoeurn

More Related