Java类的继承望大家教导我

编写三个类

我写的如下其中第一问的第六小问，第二问的第三小问和第三问非常非常不懂

修改代码如下

class Acquaintance {
    private String name;
    private char gender;
    private String phone;

    public Acquaintance() {
    }

    public Acquaintance(String name, char gender, String phone) {
        this.name = name;
        this.gender = gender;
        this.phone = phone;
    }

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

    public String getName() {
        return name;
    }

    public void setGender(char gender) {
        this.gender = gender;
    }

    public char getGender() {
        return gender;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getPhone() {
        return phone;
    }


    public String toString() {
        return "name='" + name + '\'' +
                ", gender=" + gender +
                ", phone='" + phone + '\'';
    }
}

class Friend extends Acquaintance {
    private int age;
    private String weChat;

    public void setAge(int age) {
        if (age > 0) {
            this.age = age;
        }
    }

    public int getAge() {
        return age;
    }

    public void setWeChat(String weChat) {
        this.weChat = weChat;
    }

    public String getWechat() {
        return weChat;
    }


    public Friend() {
    }
    // 2 （3）
    public Friend(String name, char gender, String phone, int age, String weChat) {
        super(name, gender, phone);
        this.age = age;
        this.weChat = weChat;
    }

    public String toString() {
        return "名字:" + this.getName() + ",性别:" + this.getGender() + ",手机号码:" + this.getPhone() + ",年龄:" + this.getAge() + ",微信号:" + this.getWechat();
    }
}

public class MyFriend {
    public static void main(String[] args) {
        Friend friend = new Friend("林清",'女',"13333330000",20,"linlily");
        friend.setName("linlinda");
        friend.setPhone("13222220000");
        friend.setAge(friend.getAge() + 1);
        System.out.println(friend.toString());
    }
}