The composite pattern enables treatnig individual objects and compositions of objects uniformly. This structural design pattern organizes objects into a tree-like structure to represent part-whole hierarchies. It allows clients to work with individual objects and composites in the same way.

In this implementation, we create a hierarchy of employees within an organization using the composite pattern.

Implementation Example

We define an Employee class that serves as both a leaf and a composite node in the organizational structure. The CompositePatternDemo class demonstrates how to build the hierarchy and display all employees.

Step 1

Create the Employee class that maintains a list of subordinate employees.

import java.util.ArrayList;
import java.util.List;

public class Employee {
    private String fullName;
    private String department;
    private int compensation;
    private List<Employee> directReports;

    public Employee(String name, String dept, int pay) {
        this.fullName = name;
        this.department = dept;
        this.compensation = pay;
        this.directReports = new ArrayList<>();
    }

    public void attach(Employee subordinate) {
        directReports.add(subordinate);
    }

    public void detach(Employee subordinate) {
        directReports.remove(subordinate);
    }

    public List<Employee> getDirectReports() {
        return directReports;
    }

    @Override
    public String toString() {
        return "Employee :[ Name : " + fullName + ", dept : " + department + ", salary :" + compensation + " ]";
    }
}

Step 2

Use the Employee class to construct and display the organizational hierarchy.

public class CompositePatternDemo {
    public static void main(String[] args) {
        Employee chiefExecutive = new Employee("John", "CEO", 30000);
        Employee salesLead = new Employee("Robert", "Head Sales", 20000);
        Employee marketingLead = new Employee("Michel", "Head Marketing", 20000);
        Employee marketingClerk1 = new Employee("Laura", "Marketing", 10000);
        Employee marketingClerk2 = new Employee("Bob", "Marketing", 10000);
        Employee salesRep1 = new Employee("Richard", "Sales", 10000);
        Employee salesRep2 = new Employee("Rob", "Sales", 10000);

        chiefExecutive.attach(salesLead);
        chiefExecutive.attach(marketingLead);
        salesLead.attach(salesRep1);
        salesLead.attach(salesRep2);
        marketingLead.attach(marketingClerk1);
        marketingLead.attach(marketingClerk2);

        System.out.println(chiefExecutive);

        for (Employee manager : chiefExecutive.getDirectReports()) {
            System.out.println(manager);
            for (Employee staff : manager.getDirectReports()) {
                System.out.println(staff);
            }
        }
    }
}

Step 3

Execute the program to see the following output:

Employee :[ Name : John, dept : CEO, salary :30000 ]
Employee :[ Name : Robert, dept : Head Sales, salary :20000 ]
Employee :[ Name : Richard, dept : Sales, salary :10000 ]
Employee :[ Name : Rob, dept : Sales, salary :10000 ]
Employee :[ Name : Michel, dept : Head Marketing, salary :20000 ]
Employee :[ Name : Laura, dept : Marketing, salary :10000 ]
Employee :[ Name : Bob, dept : Marketing, salary :10000 ]