Post on 22-Jun-2020
1
- Aggregation
- UML diagram
- Self-Referential Classes
- Generisity
Class Circlepublic 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
Class Pointpublic 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 Point3
Aggregation (הכלה)
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 .
Aggregation – example 1
Circle (c1)
center radius
p1 5.0
c1
Point (p1)
x y
7.4 9.5
p 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
5
Access to point coordinatespublic 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();
double c1CenterY = c1Center.getY();
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 Point object
This program generates the following output:
x = 7.4 y = 9.5 r = 5.0
x = 7.4 y = 9.5
We use getter methods
from Circle object
6
Rectangle definition
7
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 ).
bottomLeft
topRight
x - axis
y - axis
bottomLeft
x - axis
y - axis
width
height
Class Rectangle
8
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
Class Rectangle, cont.
9
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
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
10
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 = 18.0
Encapsulation (הכמסה)
• One of the important object-oriented techniques is hiding the
data 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 data (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
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()
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.
12
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()
UML Diagram – Example2
13
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()
● UML diagrams allow us to denote the relationships
between classes.
● In a UML diagram we can show the class member variables
and class methods.
Aggregation – example 2
Lecturer
name depCode
Alex 777lect
Student
name ID lecturer
David 1234567 lect
Student
name ID lecturer
Ronit 7654321 lect
s1 s2
14
Lecturer lect = new Lecturer(“Alex”, 777);
Student s1 = new Student(“David”, 1234567, lect);
Student s2 = new Student(“Ronit”, 7654321, lect);
Array of objects
Student [ ] arr = new Student [ 5 ];
arr[ ]
0 1 2 3 4
null null null null null
arr
arr[ ]
0 1 2 3 4
arr[0] arr[1] null null null
Lecturer lect = new Lecturer(“Alex”, 777);
arr[0] = new Student(“David”,1234567,lect);
arr[1] = new Student(“Ronit”,7654321,lect);
Student
name ID lecturer
David 1234567 lect
Student
name ID lecturer
Ronit 7654321 lect15
Insertion sort - reminder
The insertion sort algorithm works by inserting each value into a previously
sorted subset of the list.
3 9 6 1 2
3 9 6 1 2
3 6 9 1 2
1 3 6 9 2
1 2 3 6 9
3 is sorted.
Shift nothing. Insert 9.
3 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 2.
All values are sorted16
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
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
Insertion sort of integer array
How compare two
object values ?
17
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
Invoke insertSort methodpublic 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 " );
String name = reader.next();
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
We use getId() getter method
to access j student ID value
19
Class StudList - UML
StudList
int MAX_STUD
Student [ ] list
int lastPos
StudList()
void addStud(String name)
Student delStud(String name)
Student getStud(String name)
void printStudList()
UML diagram to define class
StudList
Class name
Class variables
Class methods
Constructor
20
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
21
This method adds new
student to StudList class.
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
22
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.
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 )
i++;
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
23
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.
Class StudList – delSdud testpublic 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
Class StudList – getStud testpublic 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
Self - Referential ClassesA self-referential class contains a reference member that
refers to a class object of the same class type.
public class Node
{
private int data;
private Node nextNode;
public Node( int data )
{
this.data = data;
} // class Node constructor1
public Node( int data,Node nextNode)
{
this.data = data;
this.nextNode = nextNode;
} // class Node constructor2
public void setData( int data )
{
this.data = data;
}
First constructor has only one
argument for the item; the next
field is set to null.
Field nextNode references a Node
object, an object of the same class .
Node object can be created to
point to the next Node object.
26
Class Node ,cont.public int getData()
{
return this.data;
}
public void setNext( Node nextNode )
{
this.nextNode = nextNode;
}
public Node getNext()
{
return this.nextNode;
}
public String toString()
{
return " " + this.data.toString();
}
} // end class Node
Java can link self-referential objects
together to form such useful data
structures as lists, queues, stacks and
trees.
This method allows modification of
the nextNode field.
27
Building a linked list from Node objects
Node n = new Node(9);
Node n1 = new Node(4,n);
Node n2 = new Node(5,n1);
Node
data nextNode
9 null
n
Node
data nextNode
9 null
Node
data nextNode
4
n1 n
Node
data nextNode
5
Node
data nextNode
4
Node
data nextNode
9 null
n2 n1 n
28
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 data value ");
int data = reader.nextInt();
Node n = new Node(data);
for( int i = 1; i < num; i++)
{
System.out.print("enter the data value ");
data = reader.nextInt();
n = new Node(data,n);
} // for
while( n != null )
{
String str = n.toString();
System.out.println(str);
n = n.getNext();
} //while
} // main
Input data values:
12345
Output ?
System.out.println(n);
29
Inserting a node in a linked list
Node
data nextNode
7
temp
Node
data nextNode
7
Node
data nextNode
5
n Node
data nextNode
4
Node
data nextNode
9 null
Node temp = new Node(7, n.getNext());
n.setNext(temp);
temp
30
Inserted Node
Deleting a node from a linked list
Node
data nextNode
5
Node
data nextNode
4
Node
data nextNode
9 null
n temp
Node
data nextNode
5
Node
data nextNode
4
Node
data nextNode
9 null
n temp
Node
data nextNode
5
Node
data nextNode
4 null
Node
data nextNode
9 null
n temp
1.Node temp=n.getNext();2.n.setNext( temp.getNext() );3.temp.setNext(null);
31
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
32
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
33
What are the differences?public class Node
{
private int data;
private Node nextNode;
public Node( int data )
{
this.data = data;
}
public Node(int data,Node nextNode)
{
this.data = data;
this.nextNode = nextNode;
}
public void setData( int data )
{
this.data = data;
}
public class Node
{
private String data;
private Node nextNode;
public Node( String data )
{
this.data = data;
}
public Node(String data,Node nextNode)
{
this.data = data;
this.nextNode = nextNode;
}
public void setData( String data )
{
this.data = data;
}
34
Genericity (מנגנון הגנריות)• 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
Node<T>
private T data
private Node<T> nextNode
Node(T x)
Node( T data, Node<T> nextNode)
T getData()
Node<T> getNext()
Void setData( T data)
Void setNext(Node<T> nextNode)
String toString()
constructors
Class
variables
Class methods
T is a place holder( מחזיק מקום)
35
Generic class Nodepublic class Node <T>
{
private T data;
private Node<T> nextNode;
public Node( T data )
{
this.data = data;
} // class Node<T> constructor1
public Node(T data, Node<T> nextNode)
{
this.data = data;
this.nextNode = nextNode;
} // class Node<T> constructor2
public void setData( T data )
{
this.data =data;
}
36
Generic class Node, cont.public T getData()
{
return this.data;
}
public void setNext( Node<T> nextNode )
{
this.nextNode = nextNode;
}
public Node<T> getNext()
{
return this.nextNode;
}
public String toString()
{
return " " + this.data;
}
} // end class generic Node 37
Generic class Node - implementation
Node<Point>
data nextNode
p null
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);
Point
X Y
4.0 5.0
np Node<String>
data nextNode
s null
ns
String
Hello
38
Generic class Node - implementation,cont.
np.setNext(new Node<Point>(new Point(8.0,9.0)));
ns.setNext(new Node<String>(“Java”));
Node<Point>
data nextNode
p
Node<Point>
data nextNode
null
np
Point
X Y
4.0 5.0
Point
X Y
8.0 9.0
Node<String>
data nextNode
s
Node<String>
data nextNode
null
ns
String
Hello
String
Java
39
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
40
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
Input:
Ofir
Galit
David
Ronit
Output:
Ofir -> Galit -> David -> Ronit
Base case
41
Linked list – recursion 2
42
public static int getClassLength(Node<String> s)
{
if(s.getNext( ) == null)
return 1;
return 1 + getClassLength(s.getNext( ));
} // getClassLenght
Base case
Recursive method getClassLength returns the length of
linked list.
Linked list – recursion 3
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
Recursive method getXposition returns the reference to
integer X value position in the linked list ( null if not found).