画类图

以文件夹浏览为例；

具体代码实现

//AbstractFile.java
package org.example.design008;

public abstract class AbstractFile {
    public abstract void add(AbstractFile element);
    public abstract void remove(AbstractFile element);
    public abstract void display();
}

//TextFile.java
package org.example.design008;

public class TextFile extends AbstractFile{
    public TextFile(String filename) {
        this.filename=new String();
        this.filename = filename;
    }

    private String filename;

    @Override
    public void add(AbstractFile element) {
        System.out.println("add textFile");
    }

    @Override
    public void remove(AbstractFile element) {
        System.out.println("remove textFile");
    }

    @Override
    public void display() {
        System.out.print(filename);
        System.out.println(" TextFile");
    }
}

//ImageFile.java
package org.example.design008;

import javax.xml.transform.Source;

public class ImageFile extends AbstractFile{
    public ImageFile(String filename) {
        this.filename=new String();
        this.filename = filename;
    }

    private String filename;

    @Override
    public void add(AbstractFile element) {
        System.out.println("add imageFile");
    }

    @Override
    public void remove(AbstractFile element) {
        System.out.println("remove imageFile");
    }

    @Override
    public void display() {
        System.out.print(filename);
        System.out.println(" ImageFile");
    }
}

//VideoFile.java
package org.example.design008;

public class VideoFile extends AbstractFile{
    public VideoFile(String filename) {
        this.filename=new String();
        this.filename = filename;
    }

    private String filename;

    @Override
    public void add(AbstractFile element) {
        System.out.println("add videoFile");
    }

    @Override
    public void remove(AbstractFile element) {
        System.out.println("remove videoFile");
    }

    @Override
    public void display() {
        System.out.print(filename);
        System.out.println(" VideoFile");
    }
}

//Folder.java
package org.example.design008;

import java.util.ArrayList;

public class Folder extends AbstractFile{
    public Folder(String filename) {
        this.filename=new String();
        this.filename = filename;
    }

    private String filename;
    private ArrayList<AbstractFile> list=new ArrayList<>();
    @Override
    public void add(AbstractFile element) {
        list.add(element);
        System.out.println("add folder");
    }

    @Override
    public void remove(AbstractFile element) {
        list.remove(element);
        System.out.println("remove folder");
    }

    @Override
    public void display() {
        System.out.println(filename);

        for(Object object:list){
            ((AbstractFile)object).display();
        }

        System.out.println("====Folder Display====");
    }
}

//Client.java
package org.example.design008;

public class Client {
    public static void main(String[] args) {
        AbstractFile obj1,obj2,obj3,obj4;
        Folder f1,f2,f3;

        obj1=new ImageFile("a.jpg");
        obj2=new TextFile("b.txt");

        f1=new Folder("Image_Text");
        f1.add(obj1);
        f1.add(obj2);

        obj3=new VideoFile("c.mp4");
        f2=new Folder("Image_Video");
        f2.add(obj1);
        f2.add(obj3);

        obj4=new ImageFile("d.jpg");
        f3=new Folder("Image_Text_Video");
        f3.add(f1);
        f3.add(f2);
        f3.add(obj4);

        f3.display();
    }
}