Composite Pattern

Composite Design Pattern
Advantage of Composite DP
Usage of Composite DP
UML of Composite DP
Example of Composite DP

A Composite Pattern says that just “allow clients to operate in generic manner on objects that may or may not represent a hierarchy of objects”.

Advantage of Composite Design Pattern

It defines class hierarchies that contain primitive and complex objects.
It makes easier to you to add new kinds of components.
It provides flexibility of structure with manageable class or interface.

Usage of Composite Pattern

It is used:

When you want to represent a full or partial hierarchy of objects.
When the responsibilities are needed to be added dynamically to the individual objects without affecting other objects. Where the responsibility of object may vary from time to time.

UML for Composite Pattern

Composite Pattern UML 1

Elements used in Composite Pattern:

Let’s see the 4 elements of composte pattern.

1) Component

Declares interface for objects in composition.
Implements default behavior for the interface common to all classes as appropriate.
Declares an interface for accessing and managing its child components.

2) Leaf

Represents leaf objects in composition. A leaf has no children.
Defines behavior for primitive objects in the composition.

3) Composite

Defines behavior for components having children.
Stores child component.
Implements child related operations in the component interface.

4) Client

Manipulates objects in the composition through the component interface.

Note:The work flow of above general UML is as follows.

Client uses the component class interface to interact with objects in the composition structure. If recipient is the leaf then request will be handled directly. If recipient is a composite, then it usually forwards the request to its child for performing the additional operations.

Example of Composite Pattern

We can easily understand the example of composite design pattern by the UML diagram given below:

Composite Pattern UML 2

Implementation of above UML:

Step 1

Create an Employee interface that will be treated as a component.

 // this is the Employee interface i.e. Component. public interface Employee { public  int getId(); public String getName(); public double getSalary();        public void print(); public void add(Employee employee);        public void remove(Employee employee);        public Employee getChild(int i); }// End of the Employee interface. 

Step 2

Create a BankManager class that will be treated as a Composite and implements Employee interface.

File: BankManager.java

 // this is the BankManager class i.e. Composite. import java.util.ArrayList; import java.util.Iterator; import java.util.List; public class BankManager implements Employee {  private int id;  private String name;  private double salary;   public BankManager(int id,String name,double salary) {   this.id=id;    this.name = name;   this.salary = salary;  }          List<Employee> employees = new ArrayList<Employee>();  @Override  public void add(Employee employee) {     employees.add(employee);  }         @Override  public Employee getChild(int i) {   return employees.get(i);  }  @Override  public void remove(Employee employee) {   employees.remove(employee);  }  @Override  public int getId()  {   return id;  }  @Override  public String getName() {   return name;  }     @Override  public double getSalary() {   return salary;  }  @Override  public void print() {   System.out.println(“==========================”);   System.out.println(“Id =”+getId());   System.out.println(“Name =”+getName());   System.out.println(“Salary =”+getSalary());   System.out.println(“==========================”);      Iterator<Employee> it = employees.iterator();          while(it.hasNext())  {         Employee employee = it.next();         employee.print();      }  } }// End of the BankManager class. 

Step 3

Create a Cashier class that will be treated as a leaf and it will implement to the Employee interface.

File: Cashier.java

 public  class Cashier implements Employee{ /*      In this class,there are many methods which are not applicable to cashier because      it is a leaf node.  */     private int id;             private String name;     private double salary;     public Cashier(int id,String name,double salary)  {         this.id=id;         this.name = name;         this.salary = salary;     }     @Override     public void add(Employee employee) {         //this is leaf node so this method is not applicable to this class.     }     @Override     public Employee getChild(int i) {         //this is leaf node so this method is not applicable to this class.         return null;     }     @Override public int getId() { // TODO Auto-generated method stub return id;     }     @Override     public String getName() {         return name;     }     @Override     public double getSalary() {         return salary;     }     @Override     public void print() {         System.out.println(“==========================”);         System.out.println(“Id =”+getId());         System.out.println(“Name =”+getName());         System.out.println(“Salary =”+getSalary());         System.out.println(“==========================”);     }     @Override     public void remove(Employee employee) {         //this is leaf node so this method is not applicable to this class.     } } 

Step 4

Create a Accountant class that will also be treated as a leaf and it will implement to the Employee interface.

File: Accountant.java

 public class Accountant implements Employee{ /*     In this class,there are many methods which are not applicable to cashier because     it is a leaf node. */     private int id;     private String name;     private double salary;    public Accountant(int id,String name,double salary)  {       this.id=id;        this.name = name;        this.salary = salary;    }    @Override    public void add(Employee employee) {        //this is leaf node so this method is not applicable to this class.    }    @Override    public Employee getChild(int i) {        //this is leaf node so this method is not applicable to this class.        return null;    }    @Override public int getId() { // TODO Auto-generated method stub return id;    }    @Override    public String getName() {        return name;    }    @Override    public double getSalary() {        return salary;    }    @Override    public void print() {        System.out.println(“=========================”);        System.out.println(“Id =”+getId());        System.out.println(“Name =”+getName());        System.out.println(“Salary =”+getSalary());        System.out.println(“=========================”);    }   @Override    public void remove(Employee employee) {        //this is leaf node so this method is not applicable to this class.    } }  

Step 5

Create a CompositePatternDemo class that will also be treated as a Client and ii will use the Employee interface.

File: CompositePatternDemo.java

 public class CompositePatternDemo { public static void main(String args[]){  Employee emp1=new Cashier(101,”Sohan Kumar”, 20000.0);  Employee emp2=new Cashier(102,”Mohan Kumar”, 25000.0);  Employee emp3=new Accountant(103,”Seema Mahiwal”, 30000.0);   Employee manager1=new BankManager(100,”Ashwani Rajput”,100000.0);      manager1.add(emp1);   manager1.add(emp2);   manager1.add(emp3);   manager1.print();         } } 

download this composite pattern Example

Output

 ========================== Id =100 Name =Ashwani Rajput Salary =100000.0 ========================== ========================== Id =101 Name =Sohan Kumar Salary =20000.0 ========================== ========================== Id =102 Name =Mohan Kumar Salary =25000.0 ========================== ========================= Id =103 Name =Seema Mahiwal Salary =30000.0 ========================= 

Next TopicDecorator Pattern

Composite Pattern

Composite Pattern

Advantage of Composite Design Pattern

Usage of Composite Pattern

UML for Composite Pattern

Elements used in Composite Pattern:

1) Component

2) Leaf

3) Composite

4) Client

Example of Composite Pattern

Implementation of above UML:

Step 1

Step 2

Step 3

Step 4

Step 5

Output

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