Composite

🌿 Composite

Composite is a structural design pattern that lets you compose objects into tree structures and then work with these structures as if they were individual objects.

Applicablity

Use the Composite pattern when

• you want to represent part-whole hierarchies ofobjects.
• you want clients to be able to ignore the difference between compositionsof objects and individual objects.Clients will treat all objectsin the composite structure uniformly.

General structure

• Component :
  • declares the interface for objectsin the composition.
  • implements default behavior for the interface common to all classes, as appropriate.
  • declares an interface for accessing and managing its child components.
  • (optional) defines an interface for accessing a component's parent in the recursive structure, and implements it if that's appropriate.
• Leaf :
  • represents leaf objects in the composition. A leaf has no children.
  • defines behavior for primitive objects in the composition.
• Composite :
  • defines behavior for components having children.
  • stores child components.
  • implements child-related operations in the Component interface.
• Client :
  • manipulates objects in the composition through the Component interface.

Example

Every organization is composed of employees. Each of the employees has the same features i.e. has a salary, has some responsibilities, may or may not report to someone, may or may not have some subordinates etc.

• Component : Employee
• Leaf : Developer & Designer
• Composite : Organization

The code source : source folder

  public static void main(String []args){

        Employee developerOne = new Developer(100, "Developer one", "Back-end");
        Employee developerTwo = new Developer(101, "Developer two", "FullStack");
        Employee designerUI = new Designer(201, "Designer one", "UI designer");
        Organization organization = new Organization();
        organization.addEmployee(developerOne);
        organization.addEmployee(developerTwo);
        organization.addEmployee(designerUI);

        organization.showEmployeeDetails();

        // delete developer Two
        System.out.println("----------------------");
        organization.removeEmployee(developerTwo);

        organization.showEmployeeDetails();

  }

Output :

    100- Developer one Back-end
    101- Developer two FullStack
    201- Designer one UI designer
    ----------------------
    100- Developer one Back-end
    201- Designer one UI designer