具体代码

//AbstractChatroom.java
package org.example.test017;

import javax.swing.plaf.basic.BasicTreeUI;

public abstract class AbstractChatroom {
    public abstract void register(Member member);
    public abstract void sendText(String from, String to, String message);
    public abstract void sendImage(String from, String to, String image);
}

//ChatGroup.java
package org.example.test017;

import java.util.Hashtable;

public class ChatGroup extends AbstractChatroom {
    private Hashtable members = new Hashtable();

    @Override
        public void register(Member member) {
        if (!members.contains(member)) {
            members.put(member.getName(), member);
            member.setAbstractChatroom(this);
        }
    }

    @Override
        public void sendText(String from, String to, String message) {
        Member member = (Member)members.get(to);
        String newMessage = message;

        newMessage = message.replaceAll("日", "*");
        member.receiveText(from, newMessage);
    }

    @Override
        public void sendImage(String from, String to, String image) {
        Member member = (Member)members.get(to);

        if (image.length() > 5) {
            System.out.println("图片太大，发送失败！");
        }
        else {
            member.receiveImage(from, image);
        }
    }
}

//NewGroup.java
package org.example.test017;

import java.util.HashMap;
import java.util.Map;

public class NewGroup extends AbstractChatroom {
    Map<String, Member> table = new HashMap<>();

    @Override
        public void register(Member member) {
        table.put(member.getName(), member);
        member.setAbstractChatroom(this);
    }

    @Override
        public void sendText(String from, String to, String message) {
        if (message.length() > 100) {
            System.out.println("文本长度超过100，发送失败！");
        }
        else {
            Member member = table.get(to);
            if (member != null) {
                member.receiveText(from, message);
            }
        }
    }

    @Override
        public void sendImage(String from, String to, String image) {
        if (image.length() > 20) {
            System.out.println("图片大小超过20，发送失败！");
        }
        else {
            Member member = table.get(to);
            if (member != null) {
                member.receiveImage(from, image);
            }
        }
    }
}

//Member.java
package org.example.test017;

public abstract class Member {
    protected AbstractChatroom abstractChatroom;
    protected String name;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public AbstractChatroom getAbstractChatroom() {
        return abstractChatroom;
    }

    public void setAbstractChatroom(AbstractChatroom abstractChatroom) {
        this.abstractChatroom = abstractChatroom;
    }

    public abstract void sendText(String to, String message);
    public abstract void sendImage(String to, String image);

    public void receiveText(String from, String message) {
        System.out.println(from + "发送文本给" + this.name + ",内容为：" + message);
    }

    public void receiveImage(String from, String image) {
        System.out.println(from + "发送图片给" + this.name + ",内容为：" + image);
    }
}

//CommonMember.java
package org.example.test017;

public class CommonMember extends Member {
    public CommonMember(String name) {
        super(name);
    }

    @Override
        public void sendText(String to, String message) {
        System.out.println("普通会员发送信息：");
        abstractChatroom.sendText(name, to, message);
    }

    @Override
        public void sendImage(String to, String image) {
        System.out.println("普通会员不能发送图片！");
    }
}

//DiamondMember.java
package org.example.test017;

public class DiamondMember extends Member {
    public DiamondMember(String name) {
        super(name);
    }

    @Override
        public void sendText(String to, String message) {
        System.out.println("钻石会员发送信息：");
        abstractChatroom.sendText(name, to, message);
    }

    @Override
        public void sendImage(String to, String image) {
        System.out.println("钻石会员发送图片：");
        abstractChatroom.sendImage(name, to, image);
    }
}

//NewMember.java
package org.example.test017;

public class NewMember extends Member {
    public NewMember(String name) {
        super(name);
    }

    @Override
        public void sendText(String to, String message) {
        System.out.println("新会员发送文本消息：");
        abstractChatroom.sendText(name, to, message);
    }

    @Override
        public void sendImage(String to, String image) {
        System.out.println("新会员发送图片：");
        abstractChatroom.sendImage(name, to, image);
    }
}

//Client.java
package org.example.test017;

public class Client {
    public static void main(String[] args) {
        AbstractChatroom abstractChatroom = new NewGroup();
        Member m1, m2, m3;
        m1 = new NewMember("张三");
        m2 = new NewMember("李四");
        m3 = new NewMember("王五");

        abstractChatroom.register(m1);
        abstractChatroom.register(m2);
        abstractChatroom.register(m3);

        m1.sendText("李四", "早上好奥~");
        m2.sendText("张三", "早上好！");

        m2.sendImage("王五", "早上好.jpg");
        m3.sendImage("李四", "很高兴见到你~~~~~~~~~~~~~~~~~~~~~~~~~~~.jpg");
    }
}

运行结果