Composite in C#

using System; using System.Collections.Generic; namespace RefactoringGuru.DesignPatterns.Composite.Conceptual { // The base Component class declares common operations for both simple and // complex objects of a composition. abstract class Component { public Component() { } // The base Component may implement some default behavior or leave it to // concrete classes (by declaring the method containing the behavior as // "abstract"). public abstract string Operation(); // In some cases, it would be beneficial to define the child-management // operations right in the base Component class. This way, you won't // need to expose any concrete component classes to the client code, // even during the object tree assembly. The downside is that these // methods will be empty for the leaf-level components. public virtual void Add(Component component) { throw new NotImplementedException(); } public virtual void Remove(Component component) { throw new NotImplementedException(); } // You can provide a method that lets the client code figure out whether // a component can bear children. public virtual bool IsComposite() { return true; } } // The Leaf class represents the end objects of a composition. A leaf can't // have any children. // // Usually, it's the Leaf objects that do the actual work, whereas Composite // objects only delegate to their sub-components. class Leaf : Component { public override string Operation() { return "Leaf"; } public override bool IsComposite() { return false; } } // The Composite class represents the complex components that may have // children. Usually, the Composite objects delegate the actual work to // their children and then "sum-up" the result. class Composite : Component { protected List<Component> _children = new List<Component>(); public override void Add(Component component) { this._children.Add(component); } public override void Remove(Component component) { this._children.Remove(component); } // The Composite executes its primary logic in a particular way. It // traverses recursively through all its children, collecting and // summing their results. Since the composite's children pass these // calls to their children and so forth, the whole object tree is // traversed as a result. public override string Operation() { int i = 0; string result = "Branch("; foreach (Component component in this._children) { result += component.Operation(); if (i != this._children.Count - 1) { result += "+"; } i++; } return result + ")"; } } class Client { // The client code works with all of the components via the base // interface. public void ClientCode(Component leaf) { Console.WriteLine($"RESULT: {leaf.Operation()}\n"); } // Thanks to the fact that the child-management operations are declared // in the base Component class, the client code can work with any // component, simple or complex, without depending on their concrete // classes. public void ClientCode2(Component component1, Component component2) { if (component1.IsComposite()) { component1.Add(component2); } Console.WriteLine($"RESULT: {component1.Operation()}"); } } class Program { static void Main(string[] args) { Client client = new Client(); // This way the client code can support the simple leaf // components... Leaf leaf = new Leaf(); Console.WriteLine("Client: I get a simple component:"); client.ClientCode(leaf); // ...as well as the complex composites. Composite tree = new Composite(); Composite branch1 = new Composite(); branch1.Add(new Leaf()); branch1.Add(new Leaf()); Composite branch2 = new Composite(); branch2.Add(new Leaf()); tree.Add(branch1); tree.Add(branch2); Console.WriteLine("Client: Now I've got a composite tree:"); client.ClientCode(tree); Console.Write("Client: I don't need to check the components classes even when managing the tree:\n"); client.ClientCode2(tree, leaf); } } } 

Client: I get a simple component: RESULT: Leaf Client: Now I've got a composite tree: RESULT: Branch(Branch(Leaf+Leaf)+Branch(Leaf)) Client: I don't need to check the components classes even when managing the tree: RESULT: Branch(Branch(Leaf+Leaf)+Branch(Leaf)+Leaf)