- Aggregation - UML diagram - Self-Referential Classes - Generisity

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1 - Aggregation - UML diagram - Self-Referential Classes - Generisity 1

2 Class Circle public class Circle private double xcenter; // x center coordinate private double ycenter; // y center coordinate private double radius; // circles radius public Circle(double xcenter, double ycenter, double radius ) this.xcenter = xcenter; this.ycenter = ycenter; this.radius = radius; } // class Circle constructor // rest methods... } // class Circle 2

3 Class Point public class Point private double x; // x coordinate private double y; // y coordinate public Point(double x, double y) this.x = x; this.y =y; } // class Point constructor public double getx( ) return this.x; } public void printpoint() System.out.println( "x = + this.x + "y = + this.y); } // printpoint() // rest methods } // class Point 3

4 (הכלה) Aggregation public class Circle private Point center; // another object! private double radius; // circles radius public Circle( Point center, double radius ) this.center = center; this.radius = radius; } // class Point constructor public Point getcenter() return this.center; } public double getradius() return this.radius; } // rest methods Aggregation is a relationship between two classes. The aggregate class contains a reference to another class. These methods use reference center to another object Point.

5 Aggregation example 1 Point p1 = new Point(7.4,9.5); // create new point Circle c1 = new Circle(p1,5.0); // create new circle : reference to object p1 c1 Circle (c1) center radius p1 5.0 Point (p1) x y p 1 5

6 Access to point coordinates public static void main(string[ ] args) Point p1 = new Point(7.4,9.5); // create new point Circle c1 = new Circle(p1,5.0); // create new circle Point c1center = c1.getcenter(); double c1centerx = c1center.getx(); We use getter methods double c1centery = c1center.gety(); from Point object double c1radius = c1.getradius(); System.out.println( x= + c1centerx+ y= +c1centery + r= + c1radius); // another choice c1centerx = c1.getcenter(). getx(); c1centery = c1.getcenter(). gety(); p1.printpoint(); } // main We use getter methods from Circle object This program generates the following output: x = 7.4 y = 9.5 r = 5.0 x = 7.4 y = 9.5 6

7 Rectangle definition Rectangle is any quadrilateral with four right angles. The word rectangle comes from the Latin rectangulus, which is a combination of rectus ( right ) and angulus ( angle ). y - axis topright y - axis width height bottomleft x - axis bottomleft x - axis 7

8 Class Rectangle public class Rectangle private Point bottomleft; private Point topright; public Rectangle (Point bottomleft, Point topright) this.bottomleft = bottomleft; this.topright = topright; } // constructor1 public Rectangle (Point bottomleft, double width, double height) this.bottomleft = new Point(bottomLeft); this.topright = new Point(bottomLeft.getX() + width, bottomleft.gety() + height); } // constructor2 public double getarea() double width = this.topright.getx() - this.bottomleft.getx(); double height = this.topright.gety() - this.bottomleft.gety(); return width * height; } // getarea 8

9 Class Rectangle, cont. public double getperimeter() double width = this.topright.getx() - this.bottomleft.getx(); double height = this.topright.gety() - this.bottomleft.gety(); return (2 * width) + (2 * height); } // getperimeter public void move (double deltax, double deltay) this.topright.setx(this.topright.getx() + deltax); this.topright.sety(this.topright.gety() + deltay); this.bottomleft.setx(this.bottomleft.getx() + deltax); this.bottomleft.sety(this.bottomleft.gety() + deltay); } // move public String tostring() return "Rectangle:" + "\n" + "bottom-left point : " + this.bottomleft.tostring() + "\n" + "top-right point : " + this.topright.tostring(); } // tostring } // class Rectangle 9

Class Rectangle, cont. public static void main(string[] args) Point p1 = new Point(2,1); Point p2 = new Point(7,5); Rectangle rect1 = new Rectangle(p1,p2); System.out.println(rect1); double width = 6.

10 Class Rectangle, cont. public static void main(string[] args) Point p1 = new Point(2,1); Point p2 = new Point(7,5); Rectangle rect1 = new Rectangle(p1,p2); System.out.println(rect1); double width = 6.0; double height = 3.0; Rectangle rect2 = new Rectangle(p1,width,height); System.out.println(rect2); System.out.println("area = " + rect1.getarea()); System.out.println("perimeter = "+ rect2.getperimeter()); } // main Rectangle: bottom-left point : x = 2.0 y =1.0 top-right point : x = 7.0 y = 5.0 Rectangle: bottom-left point : x = 2.0 y =1.0 top-right point : x = 8.0 y = 4.0 area = 20.0 perimeter =

11 (הכמסה) Encapsulation One of the important object-oriented techniques is hiding the ( הסתרת מידע ) within the class, and making it available only through the methods. This technique is often known as encapsulation, because it seals the class's (and internal methods) safely inside the "capsule" of the class, where it can be accessed only by trusted users- i.e., by the methods of the class. The most important reason is to hide the internal implementation details of your class. If a variable is visible only in your class, you have to document it. 11

12 UML Diagram Example1 UML stands for Unified Modeling Language. It's a way to represent object-oriented applications using graphical diagrams. UML shows the classes of the system, their relationships, and the operations and attributes of the classes. Point public double x public double y Point(double x, double y) double getx() double gety() void setx(double x) void sety(double y) String tostring() Rectangle Point bottonleft Point topright Rectangle( Point bottonleft, Point topright) Rectangle( Point bottonleft, double width, double height) double getarea() double getperimeter() void move(double deltax, double deltay) String tostring() 12

13 UML Diagram Example2 UML diagrams allow us to denote the relationships between classes. In a UML diagram we can show the class member variables and class methods. Lecturer String name int depcode Lecturer(String name,int depcode) String getname() void setdepcode( int depcode) Student String name int ID Lecturer lecturer Student(String name, int ID, Lecturer lecturer) String getname() void setid( int ID) Lecturer getlecturer() 13

14 Aggregation example 2 Lecturer lect = new Lecturer( Alex, 777); Student s1 = new Student( David, , lect); Student s2 = new Student( Ronit, , lect); Student name ID lecturer David lect Student name ID lecturer Ronit lect s1 s2 lect Lecturer name depcode Alex

15 Array of objects Student [ ] arr = new Student [ 5 ]; arr arr[ ] null null null null null Lecturer lect = new Lecturer( Alex, 777); arr[0] = new Student( David, ,lect); arr[1] = new Student( Ronit, ,lect); arr[ ] arr[0] arr[1] null null null Student name ID lecturer David lect Student name ID lecturer Ronit lect 15

16 Insertion sort - reminder The insertion sort algorithm works by inserting each value into a previously sorted subset of the list is sorted. Shift nothing. Insert and 9 are sorted. Shift 9 to the right. Insert 6. 3,6 and 9 are sorted. Shift 9,6 and 3 to the right. Insert 1. 1,3,6 and 9 are sorted. Shift 9,6 and 3 to the right. Insert All values are sorted16

17 Sorting array of objects public class Student private String name; private int id; public Student( int id, String name) this.name = name; this.id = id; } // class Student constructor public int getid( ) return this.id; } // rest methods... } // class Student Insertion sort of integer array int [ ] arr = 3, 9, 6, 1, 2 }; for (int i = 1; i < arr.length; i++) int j = i; int a = arr[i]; while ( j > 0 && arr[j-1] > a) arr[j] = arr[j-1]; j--; } // block while arr[j] = a; } // block for How compare two object values? 17

18 Sorting array of objects,cont. public static void insertsort( Student [ ] arr) for (int i = 1; i < arr.length; i++) Student val = arr[i]; // reference to arr[i] int j = i; while( j>0 && ( arr[j-1].getid() > val.getid())) arr[j] = arr [j-1]; j--; } // block while arr[j] = val; } // block for } // insertsort We use only getter methods to access student ID value 18

19 Invoke insertsort method public static void main(string[ ] args) System.out.print("enter number of student "); int num = reader.nextint(); Student [ ] arr = new Student[num]; for( int i = 0; i < num; i++) System.out.print("enter student ID " ); int id = reader.nextint(); System.out.print("enter student name " ); We use getid() getter method String name = reader.next(); to access j student ID value arr[i] = new Student( id, name ); } // for insertsort(arr); // invoke insertsort method for( int j = 0; j < num; j++) System.out.println("studID = + arr[j].getid()); } // main 19

20 Class StudList - UML UML diagram to define class StudList StudList int MAX_STUD Student [ ] list int lastpos StudList() void addstud(string name) Student delstud(string name) Student getstud(string name) void printstudlist() Class name Class variables Constructor Class methods 20

21 Class StudList - implementation public class StudList public static final int MAX_STUD = 100; private Student [ ] list; // array of Student type private int lastpos; // last free position public StudList() this.list = new Student[MAX_STUD]; this.lastpos = 0; } // StudList class constructor public void addstud( Student st ) this.list[ this.lastpos ] = st; this.lastpos++; } // addstud This method adds new student to StudList class. 21

22 Class StudList implementation,cont. public Student delstud(string name) Student st = null; int i = 0; while( i < this.lastpos && this.list[i].getname().compareto(name)!= 0 ) i++; if(i < this.lastpos) st = this.list[i]; for( int k = i+1; k < this.lastpos; k++ ) this.list[k-1] = this.list[k]; this.lastpos--; this.list[this.lastpos] = null; } return st; } // delstud This method removes the student from StudList class and returns a reference to removed value. If the student does not exist in the class, the method returns null. 22

23 Class StudList implementation,cont. public Student getstud( String name ) Student st = null; int i = 0; while( i< this.lastpos && this.list[i].getname().compareto(name)!= 0 ) if(i < this.lastpos) st = this.list[i]; return st; } // getstud public void printstudlist() for( int i = 0; i< this.lastpos; i++ ) System.out.println( "ID = + this.list[i].getid() + " name = + this.list[i].getname()); } // printstudlist } // class StudList i++; This method returns a reference to a student if his name exists in the StudList class. If the student does not exist in the class, the method returns null. 23

24 Class StudList delsdud test public static void main(string[ ] args) System.out.print( Enter number of student " ); int num = reader.nextint( ); StudList stl = new StudList( ); for( int i = 0; i < num; i++) int id = reader.nextint(); String name = reader.next(); Student st = new Student(id,name); stl. addstud(st); } // for stl.printstudlist( ) ; System.out.print( Enter student name to delete " ); String nmd = reader.next( ) ; Student d = stl.delstud(nmd); if(d == null) System.out.println( Student not found!" ); else System.out.println( Student + nmd + delete" ); stl.printstudlist(); } // main 24

25 Class StudList getstud test public static void main(string[ ] args) System.out.print( Enter number of student " ); int num = reader.nextint( ); StudList stl= new StudList( ); for( int i = 0; i < num; i++) int id = reader.nextint(); String name = reader.next(); Student st= new Student( id,name); stl. addstud(st); } // for stl.printstudlist( ) ; System.out.print( Enter student name " ); String nmf = reader.next( ) ; Student f = getstud(nmf); if(f == null) System.out.println( Student not found! " ); else System.out.println( Student + nmf + found" ); } // main 25

26 Self - Referential Classes A self-referential class contains a reference member that refers to a class object of the same class type. public class Node private int ; private Node ; public Node( int ) this. = ; } // class Node constructor1 public Node( int,node ) this. = ; this. = ; } // class Node constructor2 public void setdata( int ) this. = ; } Field references a Node object, an object of the same class. First constructor has only one argument for the item; the next field is set to null. Node object can be created to point to the next Node object. 26

27 Class Node,cont. public int getdata() return this.; } public void setnext( Node ) this. = ; } public Node getnext() return this.; } public String tostring() return " " + this..tostring(); } } // end class Node This method allows modification of the field. Java can link self-referential objects together to form such useful structures as lists, queues, stacks and trees. 27

28 Linked List vs Array 28

29 Building a linked list from Node objects Node n = new Node(9); n Node 9 null Node n1 = new Node(4,n); n1 Node n Node 4 9 null Node n2 = new Node(5,n1); n2 Node n1 Node n 5 4 Node 9 null 29

30 Building a linked list from Node objects public static void main(string[ ] args) System.out.print("enter the number of nodes "); int num = reader.nextint(); // num = 5 System.out.print("enter the value "); int = reader.nextint(); Node n = new Node(); for( int i = 1; i < num; i++) System.out.print("enter the value "); = reader.nextint(); n = new Node(,n); } // for while( n!= null ) String str = n.tostring(); System.out.println(n); System.out.println(str); n = n.getnext(); } //while } // main Input values: Output? 30

31 Inserting a node in a linked list temp Node 7 Inserted Node temp Node Node temp = new Node(7, n.getnext()); 7 n Node Node Node null n.setnext(temp); 31

32 Deleting a node from a linked list n Node temp Node Node null n Node temp Node Node null n Node temp Node Node 5 4 null 9 null 1.Node temp=n.getnext(); 2.n.setNext( temp.getnext() ); 3.temp.setNext(null); 32

33 Calculate sum in a linked list public static int calcsum( Node n) int sum = 0; Node currpos = n; // reference to first node while( currpos!= null ) sum = sum + currpos.getdata(); currpos = currpos.getnext(); } // while return sum; } // calcsum 33

34 Max value position in a linked list public static Node findmaxpos( Node n) Node maxpos = n; // searching from this place n = n.getnext(); while(n!= null ) if( n.getdata() > maxpos.getdata() ) maxpos = n; n = n.getnext(); } // while return maxpos; } // findmaxpos 34

35 What are the differences? public class Node private int ; private Node ; public Node( int ) this. = ; } public Node(int,Node ) this. = ; this. = ; } public void setdata( int ) this. = ; } public class Node private String ; private Node ; public Node( String ) this. = ; } public Node(String,Node ) this. = ; this. = ; } public void setdata( String ) this. = ; } 35

36 (מנגנון הגנריות) Genericity Genericity is a mechanism to specify the types of objects that a class can work with via parameters passed at declaration-time and evaluated at compile-time. Generic programming is the creation of programming constructs that can be used with many different types. UML diagram to define generic class Node T is a place holder (מחזיק מקום ( Node<T> private T private Node<T> Node(T x) Node( T, Node<T> ) T getdata() Node<T> getnext() Void setdata( T ) Void setnext(node<t> ) String tostring() Class variables constructors Class methods 36

37 Generic class Node public class Node <T> private T ; private Node<T> ; public Node( T ) this. = ; } // class Node<T> constructor1 public Node(T, Node<T> ) this. = ; this. = ; } // class Node<T> constructor2 public void setdata( T ) this. =; } 37

38 Generic class Node, cont. public T getdata() return this.; } public void setnext( Node<T> ) this. = ; } public Node<T> getnext() return this.; } public String tostring() return " " + this.; } } // end class generic Node 38

39 Generic class Node - implementation Point p = new Point(4.0,5.0)); Node<Point> np = new Node<Point>(p); String s = Hello ; Node<String> ns = new Node<String>(s); np Node<Point> ns Node<String> p null s null Point X Y String Hello 39

40 Generic class Node - implementation,cont. np.setnext(new Node<Point>(new Point(8.0,9.0))); ns.setnext(new Node<String>( Java )); np Node<Point> Node<Point> ns Node<String> Node<String> p null s null Point Point X Y X Y String String Hello Java 40

41 Generic class Node - test public static void main(string[ ] args) System.out.print( "enter number of student " ); int num = reader.nextint( ); // num=4 System.out.print("enter the name "); String name = reader.next(); Node<String> ns = new Node<String>(name); Node<String> startpos = ns; // help variable for(int i =1; i < num; i++) System.out.print("enter the name "); name = reader.next(); ns.setnext(new Node<String>(name)); ns = ns.getnext(); } // for printclass(startpos); // recursive method (next slide) } // main 41

42 Linked list recursion 1 public static void printclass(node<string> s) System.out.print(s.getData()); if(s.getnext()!= null) System.out.print(" -> "); printclass(s.getnext()); } } // printclass Base case Input: Ofir Galit David Ronit Output: Ofir -> Galit -> David -> Ronit 42

43 Linked list recursion 2 Recursive method getclasslength returns the length of linked list. public static int getclasslength(node<string> s) if(s.getnext( ) == null) return 1; Base case return 1 + getclasslength(s.getnext( )); } // getclasslenght 43

44 Linked list recursion 3 Recursive method getxposition returns the reference to integer X value position in the linked list ( null if not found). public static Node<Integer> getxposition(node<integer> pos, int x) if( pos.getdata( ) == x ) return pos; if( pos.getnext( ) == null ) return null; return getxposition( pos.getnext( ), x); } // getposition Base case

Object-Oriented Programming Concepts

Object-Oriented Programming Concepts Object-oriented programming מונחה עצמים) (תכנות involves programming using objects An object ) represents (עצם an entity in the real world that can be distinctly identified