Composite Design Pattern

// Component
public interface FileSystemComponent {
    String getName();
    long getSize();
    void display(String indent);
}

// Leaf
public class File implements FileSystemComponent {
    private final String name;
    private final long size;

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

    @Override
    public String getName() { return name; }

    @Override
    public long getSize() { return size; }

    @Override
    public void display(String indent) {
        System.out.println(indent + "📄 " + name + " (" + size + " bytes)");
    }
}

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

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

    public void add(FileSystemComponent component) {
        children.add(component);
    }

    public void remove(FileSystemComponent component) {
        children.remove(component);
    }

    @Override
    public String getName() { return name; }

    @Override
    public long getSize() {
        // Recursively calculates total size
        return children.stream()
            .mapToLong(FileSystemComponent::getSize)
            .sum();
    }

    @Override
    public void display(String indent) {
        System.out.println(indent + "📁 " + name + " (" + getSize() + " bytes)");
        for (FileSystemComponent child : children) {
            child.display(indent + "  ");
        }
    }
}

// Client
public class FileExplorer {
    public static void main(String[] args) {
        Directory root = new Directory("root");
        Directory src = new Directory("src");
        Directory tests = new Directory("tests");

        src.add(new File("Main.java", 2048));
        src.add(new File("Utils.java", 1024));
        tests.add(new File("MainTest.java", 1536));

        root.add(src);
        root.add(tests);
        root.add(new File("README.md", 512));

        // Treat entire tree uniformly
        root.display("");
        System.out.println("Total size: " + root.getSize() + " bytes");
    }
}

// Component
public interface Employee {
    String getName();
    double getSalary();
    void displayHierarchy(String indent);
}

// Leaf — individual contributor
public class Developer implements Employee {
    private final String name;
    private final double salary;

    public Developer(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }

    @Override
    public String getName() { return name; }

    @Override
    public double getSalary() { return salary; }

    @Override
    public void displayHierarchy(String indent) {
        System.out.println(indent + "👨‍💻 " + name + " ($" + salary + ")");
    }
}

// Composite — manager with reports
public class Manager implements Employee {
    private final String name;
    private final double salary;
    private final List<Employee> reports = new ArrayList<>();

    public Manager(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }

    public void addReport(Employee employee) {
        reports.add(employee);
    }

    public void removeReport(Employee employee) {
        reports.remove(employee);
    }

    @Override
    public String getName() { return name; }

    @Override
    public double getSalary() { return salary; }

    public double getTeamCost() {
        return salary + reports.stream()
            .mapToDouble(e -> e instanceof Manager m ? m.getTeamCost() : e.getSalary())
            .sum();
    }

    @Override
    public void displayHierarchy(String indent) {
        System.out.println(indent + "👔 " + name + " ($" + salary + ") [Team Cost: $" + getTeamCost() + "]");
        for (Employee report : reports) {
            report.displayHierarchy(indent + "  ");
        }
    }
}

// Usage
public class OrgChart {
    public static void main(String[] args) {
        Manager ceo = new Manager("Alice (CEO)", 300000);

        Manager vpEng = new Manager("Bob (VP Eng)", 200000);
        vpEng.addReport(new Developer("Charlie", 150000));
        vpEng.addReport(new Developer("Diana", 140000));

        Manager vpSales = new Manager("Eve (VP Sales)", 180000);
        vpSales.addReport(new Developer("Frank", 120000));

        ceo.addReport(vpEng);
        ceo.addReport(vpSales);

        ceo.displayHierarchy("");
    }
}

// Component — UI element
public interface UIComponent {
    void render();
    void resize(int width, int height);
}

// Leaf — simple UI element
public class Button implements UIComponent {
    private final String label;

    public Button(String label) { this.label = label; }

    @Override
    public void render() {
        System.out.println("  [Button: " + label + "]");
    }

    @Override
    public void resize(int width, int height) {
        System.out.println("  Resizing button '" + label + "' to " + width + "x" + height);
    }
}

public class TextField implements UIComponent {
    private final String placeholder;

    public TextField(String placeholder) { this.placeholder = placeholder; }

    @Override
    public void render() {
        System.out.println("  [TextField: " + placeholder + "]");
    }

    @Override
    public void resize(int width, int height) {
        System.out.println("  Resizing textfield to " + width + "x" + height);
    }
}

// Composite — container of UI elements
public class Panel implements UIComponent {
    private final String name;
    private final List<UIComponent> children = new ArrayList<>();

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

    public void add(UIComponent component) { children.add(component); }

    @Override
    public void render() {
        System.out.println("[Panel: " + name + "]");
        children.forEach(UIComponent::render);
    }

    @Override
    public void resize(int width, int height) {
        System.out.println("Resizing panel '" + name + "' and all children:");
        children.forEach(c -> c.resize(width, height));
    }
}

// Usage
Panel form = new Panel("Login Form");
form.add(new TextField("Username"));
form.add(new TextField("Password"));
form.add(new Button("Submit"));

Panel page = new Panel("Main Page");
page.add(form);
page.add(new Button("Help"));

page.render(); // Renders entire tree uniformly