Composite Design Pattern

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Aliases 📌: None

Description 📚: The composite is used to handle in a uniform way both components and groups of components.

For instance,

  • A file (component) and a folder (group)
  • A leaf (component) and a branch (group)
  • ...

Each group can contain other groups and/or components.

Advantages ✅

  • Generic and uniform

Disadvantages 🚫

  • ???

Notes 📝

Java implementation

// Component (Abstract Class)
public interface FileSystemComponent {
    void getFileCount();
}

// Leaf (File)
public class File implements FileSystemComponent {
    @Override
    public int getFileCount() {
        return 1;
    }
}

// Composite (Folder)
public class Folder implements FileSystemComponent {
    private final List<FileSystemComponent> children = new ArrayList<>();
    public Folder(String name) {}

    public void addChildren(FileSystemComponent child) {
        children.add(child);
    }

    @Override
    public int getFileCount() {
        int count = 0;
        for (FileSystemComponent component : children) {
            count += component.getFileCount();
        }
        return count;
    }
}

public class Main {
    public static void main(String[] args) {
        // Creating files
        File file1 = new File("file1.txt");
        File file2 = new File("file2.txt");
        File file3 = new File("file3.txt");

        // Creating folders
        Folder rootFolder = new Folder("Root");
        Folder subFolder = new Folder("Subfolder");

        // Adding files and subfolder to the root folder
        rootFolder.addChildren(file1);
        rootFolder.addChildren(file2);
        rootFolder.addChildren(subFolder);

        // Adding a file to the subfolder
        subFolder.addChildren(file3);

        // Count files
        System.out.println("Total Files: " + rootFolder.getFileCount());
    }
}