java

In this code:

Employee is the Component.

Developer is the Leaf.

CompanyDirectory is the Composite.

We can add more specific types of employees $($like Manager, Engineer, etc.$)$ that would also implement the Employee interface. Similarly, we can create different types of directories $($like DepartmentDirectory, TeamDirectory, etc.$)$ that would inherit from CompanyDirectory.

Code:

package CompositePatternDemo;

$//$Component

interface Employee $\{$

void showEmployeeDetails$()$;

$\}$

The Employee interface defines a common operation, showEmployeeDetails$(),$ which is to be implemented by all objects in the composition. All employees, whether they are a simple developer or a composite directory, will have this operation.

package CompositePatternDemo;

import java.util.ArrayList;

import java.util.List;

$//$Composite

class CompanyDirectory implements Employee $\{$

private List employeeList $=$ new ArrayList$()$;

@Override

public void showEmployeeDetails$()\{$

for $($Employee emp : employeeList$)\{$

emp.showEmployeeDetails$()$;

$\}$

$\}$

public void addEmployee$($Employee emp$)\{$

employeeList.add$($emp$)$;

$\}$

public void removeEmployee$($Employee emp$)\{$

employeeList.remove$($emp$)$;

$\}$

$\}$

The CompanyDirectory class is a composite node $$ it can contain both leaf nodes $($like Developer$)$ and other composite nodes $($like other CompanyDirectory instances$).$ It implements the Employee interface, and manages child Employee objects $($both leaves and composites$)$ in the employeeList.

It also provides an implementation of showEmployeeDetails$(),$ which simply delegates the operation to all its children. When called on a CompanyDirectory, this method will print the details of all employees in the directory.

package CompositePatternDemo;

$//$Leaf

class Developer implements Employee $\{$

private String name;

private long empId;

private String position;

public Developer$($long empId, String name, String position$)\{$

this.empId $=$ empId;

this.name $=$ name;

this.position $=$ position;

$\}$

@Override

public void showEmployeeDetails$()\{$

System.out.println$("$Developer ID: $"+$ empId $+"$ Name: $"+$ name $+"$ Position: $"+$ position$)$;

$\}$

$\}$

The Developer class is a leaf node $$ it can't have any children. It's one of the basic building blocks of our composition. This class implements the Employee interface and provides its own implementation of showEmployeeDetails$()$ method.

Driver:

package CompositePatternDemo;

public class CompositeDriver $\{$

public static void main$($String$[]$ args$)$

$\{$

Employee dev$1=$ new Developer$(100,$ "Fred Flintstone", "Pro Developer"$)$;

Employee dev$2=$ new Developer$(101,$ "Bart Simpson", "Developer"$)$;

CompanyDirectory engDirectory $=$ new CompanyDirectory$()$;

engDirectory.addEmployee$($dev$1)$;

engDirectory.addEmployee$($dev$2)$;

engDirectory.showEmployeeDetails$()$;

$\}$

$\}$

In our driver code, we first create two Developer instances, dev$1$ and dev$2.$ We then create a CompanyDirectory instance, engDirectory, and add dev$1$ and dev$2$ to it$.$ Finally, we call showEmployeeDetails$()$ on engDirectory $$ thanks to the composite pattern, this prints the details of all employees in the directory, regardless of how many there are or how they're structured.