Code Reusability
Code reusability means reusing the existing classes.
In java code reusability is achieved by using two concepts:
1)
Composition
2)
Inheritance
Composition:
Composition means creating object of existing class as data
member of new class.
it is a has-a relationship.
example: Student has a class room, library has books and Student has a library.
Composition is achevied by in 2 techniques:
1. Association:
Here association is defined as a Sudent connot exist without ClassRoom, means you cannot create a student object without creating ClassRoom class Object.
class Student{
ClassRoom croom; //here croom object must created.
}
we seen one-to-one, one-to-many,many-many,many-one are the associations relationships in java.
2. Aggregation:
Aggregation is also has-a relationship, but here the relationship is organized is loosely.
example: the relationship b/w the Library and Student. Here a Library Object is created with out creating the Student object.
class Library{
Student stu;// it is not mandatory to exist stu objecgt.
}
//existing class defined by user1
Point.java
Package pack1;
public class Point{
public int x;
public int y;
}
Javac –d . Point.java
Note:move Point.java to pack1.
//new class defined by user2
Package pack2;
Import pack1.Point;
public class Circle {
public int radius;
public
Point center=new Point();
}
Javac -d .
Circle.java
Note: move Circle.java to pack2;
Demo.java
public class Demo {
public static void main(String[] args) {
Circle c=new Circle();
c.radius=3;
c.center.x=1;
c.center.y=2;
System.out.println(c.radious);
System.out.println(c.center.x);
System.out.println(c.center.y);
}
}
