// 痛点：客户端代码需要区分文件和目录，并分别处理
public void display(Object node) {
    if (node instanceof File) {
        // 处理文件的逻辑
        File file = (File) node;
        System.out.println("File: " + file.getName());
    } else if (node instanceof Directory) {
        // 处理目录的逻辑
        Directory dir = (Directory) node;
        System.out.println("Directory: " + dir.getName());
        // 必须遍历子节点，并对每个子节点再次进行类型判断
        for (Object child : dir.getChildren()) {
            display(child); // 递归调用，但递归的每一步都充满了if-else
        }
    }
}

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

// 1. 组件 (Component)
abstract class FileSystemComponent {
    protected String name;

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

    public String getName() {
        return name;
    }

    // 通用操作
    public abstract void display(String indent);
    public abstract long getSize();

    // 子节点管理方法（透明模式）
    // 默认实现为抛出异常，因为叶子节点不支持这些操作
    public void add(FileSystemComponent component) {
        throw new UnsupportedOperationException("Cannot add to a file.");
    }

    public void remove(FileSystemComponent component) {
        throw new UnsupportedOperationException("Cannot remove from a file.");
    }
}

// 2. 叶子 (Leaf)
class FileNode extends FileSystemComponent {
    private long size;

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

    @Override
    public void display(String indent) {
        System.out.println(indent + "- " + getName() + " (" + getSize() + " bytes)");
    }

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

// 3. 组合 (Composite)
class DirectoryNode extends FileSystemComponent {
    // 内部持有子节点的集合
    private List<FileSystemComponent> children = new ArrayList<>();

    public DirectoryNode(String name) {
        super(name);
    }

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

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

    @Override
    public void display(String indent) {
        System.out.println(indent + "+ " + getName());
        // 递归地显示子节点
        for (FileSystemComponent component : children) {
            component.display(indent + "  ");
        }
    }

    @Override
    public long getSize() {
        // 目录的大小是所有子节点大小的总和
        long totalSize = 0;
        for (FileSystemComponent component : children) {
            totalSize += component.getSize();
        }
        return totalSize;
    }
}

// 4. 客户端
public class CompositePatternDemo {
    public static void main(String[] args) {
        // 创建树形结构
        DirectoryNode root = new DirectoryNode("root");
        DirectoryNode documents = new DirectoryNode("documents");
        DirectoryNode pictures = new DirectoryNode("pictures");

        FileNode resume = new FileNode("resume.docx", 1024);
        FileNode photo1 = new FileNode("photo1.jpg", 2048);
        FileNode photo2 = new FileNode("photo2.png", 4096);
        DirectoryNode project = new DirectoryNode("project");
        FileNode code = new FileNode("main.java", 512);

        // 构建层级关系
        root.add(documents);
        root.add(pictures);

        documents.add(resume);
        documents.add(project);
        project.add(code);

        pictures.add(photo1);
        pictures.add(photo2);

        // 客户端统一操作，只需调用根节点的 display
        System.out.println("--- Displaying File System Structure ---");
        root.display("");
        
        System.out.println("\n--- Calculating Sizes ---");
        System.out.println("Size of 'documents' directory: " + documents.getSize() + " bytes");
        System.out.println("Total size of 'root' directory: " + root.getSize() + " bytes");
    }
}