1.创建JavaBean类

public class Friend {
    //题目要求：定义数组存储4个朋友对象
    //属性：姓名，年龄，性别，爱好
    //计算出四位朋友的平均年龄
    //统计出比平均年龄低的朋友有几个，并把信息都打印出来
    private String name;
    private int age;
    private char gender;
    private String hobby;
    //构建标准的JavaBean类
    //空参

    public Friend() {
    }
    //全参

    public Friend(String name, int age, char gender, String hobby) {
        this.name = name;
        this.age = age;
        this.gender = gender;
        this.hobby = hobby;
    }
    //成员方法

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

    public char getGender() {
        return gender;
    }

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

    public String getHobby() {
        return hobby;
    }

    public void setHobby(String hobby) {
        this.hobby = hobby;
    }
}

2.测试类

public class FriendTest {
    public static void main(String[] args) {
        //1.新建数组
        Friend[] arr = new Friend[4];
        //2.创建对象
        Friend f1 = new Friend("张三", 18, '女', "唱歌");
        Friend f2 = new Friend("李四", 20, '女', "跳舞");
        Friend f3 = new Friend("王五", 23, '男', "rap");
        Friend f4 = new Friend("赵六", 30, '男', "打篮球");
        //3.存入数组中
        arr[0] = f1;
        arr[1] = f2;
        arr[2] = f3;
        arr[3] = f4;
        //4.求平均值
        int sum = 0;
        for (int i = 0; i < arr.length; i++) {
            Friend friend = arr[i];
            sum = sum + friend.getAge();
        }
        int avg = sum / arr.length;
        System.out.println("四位朋友年龄的平均值为：" + avg);
        //5.统计年龄比平均值低的有几个，并打印信息
        int count = 0;
        for (int i = 0; i < arr.length; i++) {
            Friend friend = arr[i];
            if (friend.getAge() < avg) {
                count++;
            }
        }
        System.out.println("年龄比平均值低的共有" + count + "位");
        //6.打印信息
        System.out.println("分别为：");
        for (int i = 0; i < arr.length; i++) {
            Friend friend = arr[i];
            if (friend.getAge() < avg) {
                count++;
                System.out.println(friend.getName() + ", " + friend.getAge() + ", " + friend.getGender() + ", " + friend.getHobby());
            }
        }
    }
}

3.运行结果