2009年下半年

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

abstract class AbstractFile { // (1)
    protected String name;

    public void printName() {
        System.out.println(name);
    }

    public abstract boolean addChild(AbstractFile file);

    public abstract boolean removeChild(AbstractFile file);

    public abstract List<AbstractFile> getChildren();
}

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

    public boolean addChild(AbstractFile file) {
        return false;
    }

    public boolean removeChild(AbstractFile file) {
        return false;
    }

    public List<AbstractFile> getChildren() {
        return null; // (2) 文件没有子节点
    }
}

class Folder extends AbstractFile {
    private List<AbstractFile> childList;

    public Folder(String name) {
        this.name = name;
        this.childList = new ArrayList<AbstractFile>();
    }

    public boolean addChild(AbstractFile file) {
        return childList.add(file);
    }

    public boolean removeChild(AbstractFile file) {
        return childList.remove(file);
    }

    public List<AbstractFile> getChildren() { // (3)
        return childList;                     // (4)
    }
}

public class Client {
    public static void main(String[] args) {
        // 创造一个树形的文件/目录结构
        AbstractFile rootFolder = new Folder("c:\\");
        AbstractFile compositeFolder = new Folder("composite");
        AbstractFile windowsFolder = new Folder("windows");
        AbstractFile file = new File("TestComposite.java");

        rootFolder.addChild(compositeFolder);
        rootFolder.addChild(windowsFolder);
        compositeFolder.addChild(file);

        // 打印目录文件树
        printTree(rootFolder);
    }

    private static void printTree(AbstractFile ifile) {
        ifile.printName();
        List<AbstractFile> children = ifile.getChildren();
        if (children == null) return; // 注意：children 不能大写
        for (AbstractFile file : children) {
            printTree(file); // (5) 递归打印子树
        }
    }
}