# Composite

Paul Tomoiu

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Examples,

Design patterns

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Published 2022-12-03

This tutorial explains to you the design pattern named Composite (which is a Structural Pattern).

# Composite Pattern - theory

Composite design pattern in Java allows you to have a tree structure and ask each node in the tree structure to perform a task. This pattern produce a hierarchical tree which can be accessed by using a uniform method.

Take a look at the following UML diagram representing the Composite design pattern:

# Composite Pattern - example

Here is that example using the Composite Design Pattern in Java:

package composite.java.example;
 
import java.util.ArrayList;
import java.util.List;
 
public class Employee {
   private String name;
   private String job;
    
   private List<Employee> subordinates;
 
   public Employee(String name, String job) {
      this.name = name;
      this.job = job;
 
      subordinates = new ArrayList<Employee>();
   }
 
   public void add(Employee e) {
      subordinates.add(e);
   }
 
   public void remove(Employee e) {
      subordinates.remove(e);
   }
 
   public List<Employee> getSubordinates(){
     return subordinates;
   }
 
   public String toString(){
      return ("( Name : " + name + ",   Job : " + job +" )");
   }   
}

package composite.java.example;
 
public class JavaCompositePatternExample {
     public static void main(String[] args) {
            
          Employee pres = new Employee("Greg","President");
          Employee vp1 = new Employee("Dana","Vice-President");
          Employee dir1 = new Employee("Mark","Director");
          Employee dir2 = new Employee("Emanuil","Director");
          Employee mark1 = new Employee("Laura","Marketing");
 
          pres.add(vp1);
          vp1.add(dir1);
          vp1.add(dir2);
          dir1.add(mark1);
 
           
          for (Employee emp1 : pres.getSubordinates()) {
             System.out.println("Level1: "+emp1);
              
             for (Employee emp2 : emp1.getSubordinates()) {
                System.out.println("Level2: "+emp2);
             }
          }     
       }
    }

When you run this example you will receive the following result: