Java集合练习题 求学生对象的平均年龄及按班级求平均分数

有如下Student 对象，
private String name;
private int age;
private int score;
private String classNum;

其中，classNum 表示学生的班号，例如“class05”。 有如下List

List list = new ArrayList();

list.add(new Student(“Tom”, 18, 100, “class05”));
list.add(new Student(“Jerry”, 22, 70, “class04”));
list.add(new Student(“Owen”, 25, 90, “class05”));
list.add(new Student(“Jim”, 30,80 , “class05”));
list.add(new Student(“Steve”, 28, 66, “class06”));
list.add(new Student(“Kevin”, 24, 100, “class04”));

在这个list 的基础上，完成下列要求：
1） 计算所有学生的平均年龄
2） 计算各个班级的平均分

 

主类：

import java.util.ArrayList;

public class TestDay17_1_2 {

    public static void main(String[] args) {
        ArrayList<TestDay17_1_2_Student> al = new ArrayList<>();

        al.add(new TestDay17_1_2_Student("Tom", 18, 100, "class05"));
        al.add(new TestDay17_1_2_Student("Jerry", 22, 70, "class04"));
        al.add(new TestDay17_1_2_Student("Owen", 25, 90, "class05"));
        al.add(new TestDay17_1_2_Student("Jim", 30, 80, "class05"));
        al.add(new TestDay17_1_2_Student("Steve", 28, 66, "class06"));
        al.add(new TestDay17_1_2_Student("Kevin", 24, 100, "class04"));

        // 计算平均年龄
        //定义总年龄及人数变量
        int sumAge = 0;
        int count = 0;
        //遍历集合 总年龄累加、人数自增
        for (TestDay17_1_2_Student s : al) {
            sumAge += s.getAge();
            count++;
        }
        //计算并输出平均年龄
        double averageAge = (sumAge * 1.0) / count;
        System.out.println("平均年龄是：" + averageAge);

        //计算各班级平均分
        // 创建储存计算分数的集合
        ArrayList<TestDay17_1_2_Score> alscore = new ArrayList<>();
        // 遍历班级唯一插入成绩对象

        for (int i = 0; i < al.size(); i++) {
            //过去当前学生对象
            TestDay17_1_2_Student student = al.get(i);
            boolean flag = false;//标记没有重复班级名称
            for (int j = 0; j < alscore.size(); j++) {
                //获取当前班级成绩对象
                TestDay17_1_2_Score score = alscore.get(j);
                //判断班级名称是否重复
                if (student.getClassNum().equals(score.getClassName())) {
                    //重复标记设为真
                    flag = true;
                    //修改当前成绩对象中分数和人数信息并跳出内循环
                    score.setStudentNum(score.getStudentNum()+1);
                    score.setSumScore(score.getSumScore() + student.getScore());
                    break;
                }
            }
            
            //判断flag如果为假（没有重复）则添加一个新的成绩对象
            if (!flag) {
                alscore.add(new TestDay17_1_2_Score(student.getClassNum(),1,student.getScore()));
            }
        }
        for (TestDay17_1_2_Score score : alscore) {
            System.out.println(score.toString());
        }
    }
}

学生类：

public class TestDay17_1_2_Student {

    private String name;  
    private int age;  
    private int score;  
    private String classNum;
    public TestDay17_1_2_Student() {
        super();
        // TODO Auto-generated constructor stub
    }
    public TestDay17_1_2_Student(String name, int age, int score, String classNum) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
        this.classNum = classNum;
    }
    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 int getScore() {
        return score;
    }
    public void setScore(int score) {
        this.score = score;
    }
    public String getClassNum() {
        return classNum;
    }
    public void setClassNum(String classNum) {
        this.classNum = classNum;
    }
}

成绩类：

public class TestDay17_1_2_Score {

    private String className;
    private int studentNum;
    private int sumScore;
    
    public TestDay17_1_2_Score() {
        super();
        // TODO Auto-generated constructor stub
    }
    public TestDay17_1_2_Score(String className, int studentNum, int sumScore) {
        super();
        this.className = className;
        this.studentNum = studentNum;
        this.sumScore = sumScore;
    }
    public String getClassName() {
        return className;
    }
    public void setClassName(String className) {
        this.className = className;
    }
    public int getStudentNum() {
        return studentNum;
    }
    public void setStudentNum(int studentNum) {
        this.studentNum = studentNum;
    }
    public int getSumScore() {
        return sumScore;
    }
    public void setSumScore(int sumScore) {
        this.sumScore = sumScore;
    }
    
    public double getAverageScore() {
        return (this.sumScore * 1.0) / this.studentNum;
    }
    
    @Override
    public String toString() {
        double averageScore = this.getAverageScore();
        String className = this.getClassName();
        int studentNum = this.getStudentNum();
        int sumScore = this.getSumScore();
        return
            (new StringBuffer()).append(className)
            .append("班级有").append(studentNum)
            .append("个同学，总分：").append(sumScore)
            .append("，平均分：").append(averageScore).toString()
        ;
    }
}