访问数据结构并处理数据

1 - 表示访问者的抽象类, 它访问文件和文件夹

public abstract class Visitor {
    public abstract void visit(File file);
    public abstract void visit(Directory directory);
}

2 - 表示数据结构的接口, 它接受访问者的访问

public interface Element {
    public abstract void accept(Visitor v);
}

3 - Visitor类的子类, 显示文件和文件夹一览

public class ListVisitor extends Visitor{
    private String currentDir = "";

    @Override
    public void visit(File file) {
        System.out.println(currentDir + "/" + file);
    }

    @Override
    public void visit(Directory directory) {
        System.out.println(currentDir + "/" + directory);
        String saveDir = currentDir;
        currentDir = currentDir + "/" + directory.getName();
        Iterator it = directory.iterator();
        while (it.hasNext()){
            Entry entry = (Entry)it.next();
            entry.accept(this);
        }
        currentDir = saveDir;
    }
}

4 - 抽象类, File类和Directory类的父类, 实现了Element接口

public abstract class Entry implements Element{
    public abstract String getName();   // 获取名字
    public abstract int getSize();      // 获取大小
    public Entry add(Entry entry) throws FileTreatMeantException { // 加入条目目录
        throw new FileTreatMeantException();
    }

    public Iterator iterator() throws FileTreatMeantException { // 生成Iterator
        throw new FileTreatMeantException();
    }
                                                        // 显示条目一览
    @Override                                           // 显示代表类的文字
    public String toString(){
        return getName() + " (" + getSize() + ")";
    }
}

5 - 表示文件的类

public class File extends Entry{
    private String name;
    private int size;

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

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

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

    @Override
    public void accept(Visitor v) {
        v.visit(this);
    }
}

6 - 表示文件夹的类

public class Directory extends Entry{
    private String name;
    private ArrayList directory = new ArrayList();
    public Directory(String name){
        this.name = name;
    }

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

    @Override
    public int getSize() {
        int size = 0;
        for (Object o : directory) {
            Entry entry = (Entry) o;
            size += entry.getSize();
        }
        return size;
    }

    public Entry add(Entry entry){
        directory.add(entry);
        return this;
    }

    public Iterator iterator(){
        return directory.iterator();
    }

    @Override
    public void accept(Visitor v) {
        v.visit(this);
    }
}

7 - 表示向文件中增加Entry时发生的异常的类

public class FileTreatMeantException extends RuntimeException{

    public FileTreatMeantException(){
    }

    public FileTreatMeantException(String msg){
        super(msg);
    }
}

8 - 测试程序行为的类

public class Main {
    public static void main(String[] args) {
        try {
            System.out.println("Making root entries...");
            Directory rootDir = new Directory("root");
            Directory binDir = new Directory("bin");
            Directory tmpDir = new Directory("tmp");
            Directory usrDir = new Directory("usr");
            rootDir.add(binDir);
            rootDir.add(tmpDir);
            rootDir.add(usrDir);
            binDir.add(new File("vi", 10000));
            binDir.add(new File("latex", 20000));
            rootDir.accept(new ListVisitor());

            System.out.println("");
            System.out.println("Making user entries...");
            Directory yuki = new Directory("yuki");
            Directory hanako = new Directory("hanako");
            Directory tomura = new Directory("tomura");
            usrDir.add(yuki);
            usrDir.add(hanako);
            usrDir.add(tomura);
            yuki.add(new File("diary.html", 100));
            yuki.add(new File("Composite.java", 200));
            hanako.add(new File("memo.tex", 300));
            tomura.add(new File("game.doc", 400));
            tomura.add(new File("junk.mail", 500));
            rootDir.accept(new ListVisitor());

        }catch (FileTreatMeantException e){
            e.printStackTrace();
        }
    }
}

9 - 输出样例

Making root entries...
/root (30000)
/root/bin (30000)
/root/bin/vi (10000)
/root/bin/latex (20000)
/root/tmp (0)
/root/usr (0)

Making user entries...
/root (31500)
/root/bin (30000)
/root/bin/vi (10000)
/root/bin/latex (20000)
/root/tmp (0)
/root/usr (1500)
/root/usr/yuki (300)
/root/usr/yuki/diary.html (100)
/root/usr/yuki/Composite.java (200)
/root/usr/hanako (300)
/root/usr/hanako/memo.tex (300)
/root/usr/tomura (900)
/root/usr/tomura/game.doc (400)
/root/usr/tomura/junk.mail (500)