Composit Pattern Example

Composit design pattern is one of the structural pattern. You can use this pattern for maintaining hierarchy of objects. Here I am going to explain example with college staff hierarchy. You can follo steps to get working example.

1. Create StaffMember class as given below. Here remember that composit pattern class will always have list of objects of its own type.
import java.util.ArrayList;
import java.util.List;

public class StaffMember {
    private int ID;
    private String name, desg;
    public List<StaffMember> subMember;
   
    public StaffMember(int ID, String name, String desg) {
        this.ID = ID;
        this.name = name;
        this.desg = desg;
        subMember = new ArrayList<StaffMember>();
    }//StaffMember
   
    public void addSubMember(StaffMember staffMember) {
        subMember.add(staffMember);
    }//addSubMember
   
    public List<StaffMember> getSubMember(StaffMember staffMember) {
        return subMember;
    }//getSubMember
   
    public String toString() {
        return "\nID : " + ID + "\tName : " + name + "\tDesg : " + desg;
    }//toString
   
}//class StaffMember

2. Now create Main class for demo as given below.
import java.util.List;

public class Main {
    public static void main(String args[]) {
        StaffMember headMaster = new StaffMember(1, "A", "HeadMaster");
        StaffMember subHeadMaster = new StaffMember(2, "B", "Sub-HeadMaster");
        StaffMember supervisor1 = new StaffMember(3, "C", "Supervisor-1");
        StaffMember supervisor2 = new StaffMember(4, "D", "Supervisor-2");
        StaffMember teacher1 = new StaffMember(5, "E", "Teacher-1");
        StaffMember teacher2 = new StaffMember(6, "F", "Teacher-2");
        StaffMember teacher3 = new StaffMember(7, "G", "Teacher-3");
        StaffMember teacher4 = new StaffMember(8, "H", "Teacher-4");
        headMaster.addSubMember(subHeadMaster);
        subHeadMaster.addSubMember(supervisor1);
        subHeadMaster.addSubMember(supervisor2);
        supervisor1.addSubMember(teacher1);
        supervisor1.addSubMember(teacher2);
        supervisor2.addSubMember(teacher3);
        supervisor2.addSubMember(teacher4);
       
        System.out.print("\nHead master hierarchy : ");
        printHierarchy(headMaster);
        System.out.print("\n=========================================");
        System.out.print("\nSub head master hierarchy : ");
        printHierarchy(subHeadMaster);
        System.out.print("\n=========================================");
        System.out.print("\nSupervisor 1 hierarchy : ");
        printHierarchy(supervisor1);
        System.out.print("\n=========================================");
        System.out.print("\nSupervisor 2 hierarchy : ");
        printHierarchy(supervisor2);
       
    }//PSVM
   
    public static void printHierarchy(StaffMember staffMember) {
        System.out.print(staffMember.toString());
        List<StaffMember> member = staffMember.getSubMember(staffMember);
        for(int i = 0; i < member.size(); i++) {
            printHierarchy(member.get(i));
        }//for i
    }//printHierarchy
   
}//class Main

Now you modify StaffMember class for additional information like you can store parent of that object. You can put some checks when adding member. You can add method for removing member from hierarchy.