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Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
Java OO Revisited
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Java OO Revisited

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    • 1. Object  Orientated  Programming  with   Java   Jussi  Pohjolainen   Tampere  University  of  Applied  Sciences  
    • 2. Object  Orientated  Concepts   •  Class   •  Object   •  Inheritance   •  Constructors   •  Abstract  class   •  Interface   •  Polymorphism  
    • 3. Class   class Student { private String name; public Student(String name) { this.name = name; } public void setName(String name) { this.name = name } public void getName() { return name; } }
    • 4. CreaAng  objects   Student jack = new Student(“Jack”); Student bill = new Student(“Bill”); System.out.println( jack.getName() ); System.out.println( bill.getName() );
    • 5. Reference?   Student jack = new Student(“Jack”); Student bill = jack; jack.setName(“Lisa”); // What is the output? System.out.println(bill.getName());
    • 6. Reference   •  In  Java,  every  object  is  passed  by  reference   •  If  you  want  to  clone  a  object,  you  use  special   techniques  (later  on  the  material)  
    • 7. Inheritance   class Person { private String name; ... } class Student extends Person { private int id; ... }
    • 8. Constructors   class Person { private String name; public Person() { System.out.println(“Person”); } } class Student extends Person { private int id; public Student() { System.out.println(“Student”); } } // What is the output? Student s = new Student();
    • 9. Default  Constructor   •  If  programmer  does  not  define  a  constructor,  Java   creates  a  default  constructor:   class Person { } => class Person { public Person() { super(); } }
    • 10. Default  Constructor   class Person { private String name; public Person() { System.out.println(“Person”); } } class Student extends Person { private int id; } // What is the output? Student s = new Student();
    • 11. Default  Constructor  Problem   class Person { private String name; public Person(String name) { System.out.println(“Person”); } } class Student extends Person { private int id; } // What is the output? Student s = new Student();
    • 12. Abstract  Class   •  You  cannot  create  a  object  from  abstract  class   •  Abstract  class  may  contain  abstract  method   •  Abstract  method  is  a  method  declaraAon  which   must  be  implemented  in  inherited  classes  
    • 13. Abstract  Class   abstract class Graphic { abstract double calculateSurfaceArea(); } class Circle extends Graphic { private int radius; double calculateSurfaceArea() { ... } }
    • 14. Abstract  Class   abstract class A { abstract void m(); } abstract class B extends A { // What is the implementation of the class B? }
    • 15. Interface   •  Interface  is  a  abstract  class  that  contain  only   abstract  methods   •  Interface  can  contain  also  public  staAc  final   variables   •  Class  can  inherit  only  one  class,  but  it  can   implement  many  interfaces  
    • 16. Interface   interface class A { public void m(); } class B implements A { public void m() { ... } }
    • 17. Polymorphism   •  Declaring  a  object:   –  Graphic c;! •  IniAalizing  the  object:   –  c = new Graphic();! •  This  is  also  possible:   –  c = new Circle();! –  c = new Rect();! •  If  Circle and  Rect are  inherited  from  Graphic!
    • 18. Polymorphism   class Polymorphism { public static void main(String [] args) { // What are the possible objects to be passed? method(??) } public static void method(Graphic c) { ... } }
    • 19. Polymorphism   interface R { ... } class Polymorphism { public static void main(String [] args) { // What are the possible objects to be passed? method(??) } public static void method(R r) { ... } }
    • 20. Cloning   class Person implements Cloneable { private name; public Person(String name) { this.name = name; } public Object clone() { return new Person(this.name); } } Person a = new Person(“jack”); Person b = a.clone();
    • 21. Equals   // What happens here? Student jack1 = new Student(“Jack”); Student jack2 = new Student(“Jack”); System.out.println( jack1 == jack2 ); // true or false? System.out.println( jack1.equals(jack2) ); // ?

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