Composite

It allow you to treat individual objects and compositions of objects uniformly. It is useful when you have to work with tree-like hierarchical structures, where individual objects (leaf nodes) and compositions of objects (composite nodes) are part of the same hierarchy.

Structure

• Component: This is the interface or abstract class that declares the operations common to both leaf and composite nodes.
• Leaf: Represents individual objects that cannot have children. It implements the Component interface.
• Composite: Represents objects that can contain other Component objects (both leaf and composite). It implements the Component interface and contains methods for adding, removing, and managing child components

Example

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

// Component interface
interface FileSystemComponent {
    void showDetails();
}

// Leaf class: File
class File implements FileSystemComponent {
    private String name;

    public File(String name) {
        this.name = name;
    }

    @Override
    public void showDetails() {
        System.out.println("File: " + name);
    }
}

class Folder implements FileSystemComponent {
    private String name;
    private List<FileSystemComponent> components = new ArrayList<>();

    public Folder(String name) {
        this.name = name;
    }

    // Adding a new component (File or Folder)
    public void addComponent(FileSystemComponent component) {
        components.add(component);
    }

    // Removing a component
    public void removeComponent(FileSystemComponent component) {
        components.remove(component);
    }

    // Show details of the folder and its contents
    @Override
    public void showDetails() {
        System.out.println("Folder: " + name);
        for (FileSystemComponent component : components) {
            component.showDetails();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        // Creating individual files (leaf nodes)
        FileSystemComponent file1 = new File("File1.txt");
        FileSystemComponent file2 = new File("File2.txt");
        FileSystemComponent file3 = new File("File3.jpg");

        // Creating folders (composite nodes)
        Folder folder1 = new Folder("Documents");
        Folder folder2 = new Folder("Images");

        // Adding files to folders
        folder1.addComponent(file1);  // Adding file1 to Documents
        folder1.addComponent(file2);  // Adding file2 to Documents
        folder2.addComponent(file3);  // Adding file3 to Images

        // Creating the root folder and adding sub-folders
        Folder rootFolder = new Folder("Root");
        rootFolder.addComponent(folder1);  // Adding Documents folder to Root
        rootFolder.addComponent(folder2);  // Adding Images folder to Root

        // Displaying the file system structure
        rootFolder.showDetails();
    }
}