collection.sort用的是啥排序算法

Posted 2023-05-05

现在java8帮你封装了一把，可以不用Colltion的sort方法啦，很简单 list.stream.sorted(); 就可以直接排序啦，对于基本类型的数据 若是一个对象的集合，比如List list这类的集合，假如User中有一个name一个属性，那么按照User的name进行排序的话 参考技术A stream.sorted结束操作也是用的Arrays.sort(T[],)，即TimSort.sort使用的插入+归并排序算法。

数据结构-排序（选做） 20175204

数据结构-排序（选做）

任务要求

在数据结构和算法中，排序是很重要的操作，要让一个类可以进行排序，有两种方法：

• 有类的源代码，针对某一成员变量排序，让类实现Comparable接口,调用Collection.sort(List)
• 没有类的源代码，或者多种排序，新建一个类，实现Comparator接口 调用Collection.sort(List, Compatator)

针对下面的Student类，使用Comparator编程完成以下功能：

1. 在测试类StudentTest中新建学生列表，包括自己和学号前后各两名学生，共5名学生,给出运行结果（排序前，排序后）
2. 对这5名同学分别用学号和总成绩进行增序排序，提交两个Comparator的代码
3. 课下提交代码到码云

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给定student类

class Student {
private String id;//表示学号
private String name;//表示姓名
private int age;//表示年龄
private double computer_score;//表示计算机课程的成绩
private double english_score;//表示英语课的成绩
private double maths_score;//表示数学课的成绩
private double total_score;// 表示总成绩
private double ave_score; //表示平均成绩
public Student(String id, String name){
    this.id = id;
    this.name = name;

}
public Student(String id, String name, char sex, int age){
this(id, name);
this.sex = sex;
this.age = age;
}
public String getId(){
return id;
}//获得当前对象的学号，
public double getComputer_score(){
return computer_score;
}//获得当前对象的计算机课程成绩,
public double getMaths_score(){
return maths_score;
}//获得当前对象的数学课程成绩,
public double getEnglish_score(){
return english_score;
}//获得当前对象的英语课程成绩,
public void setId(String id){
this.id=id;
}// 设置当前对象的id值,
public void setComputer_score(double computer_score){
this.computer_score=computer_score;
}//设置当前对象的Computer_score值,
public void setEnglish_score(double english_score){
this.english_score=english_score;
}//设置当前对象的English_score值,
public void setMaths_score(double maths_score){
this.maths_score=maths_score;
}//设置当前对象的Maths_score值,
public double getTotalScore(){
return computer_score+maths_score+english_score;
}// 计算Computer_score, Maths_score 和English_score 三门课的总成绩。
public double getAveScore(){
return getTotalScore()/3;
}// 计算Computer_score, Maths_score 和English_score 三门课的平均成绩。
}
class Undergraduate extends Student{
private String classID;
public Undergraduate(String id, String name, char sex, int age,String classID){
super(id,name,sex,age);
this.classID=classID;
}
public String getClassID(){
return classID;
}
public void setClassID(String classID){
this.classID=classID;
}
}

---

修改增加student类

 * task2
 *
 * @author 20175204
 * @date 2019/5/5
 */
class Student {
    private char sex = 0;
    private String id;//表示学号
    private String name;//表示姓名
    private int age;//表示年龄
    private double computer_score;//表示计算机课程的成绩
    private double english_score;//表示英语课的成绩
    private double maths_score;//表示数学课的成绩
    private double total_score;// 表示总成绩
    private double ave_score; //表示平均成绩
    public int xuehao, mingci;
    public double a1, a2, a3;
    Student(int xuehao, String name, int age, double a1, double a2, double a3) {
        this.xuehao = xuehao;
        this.name = name;
        this.age = age;
        this.a1 = a1;
        this.a2 = a2;
        this.a3 = a3;
    }
    public Student(String id, String name) {
        this.id = id;
        this.name = name;
    }
    public Student(String id, String name, char sex, int age) {
        this(id, name);
        this.sex = sex;
        this.age = age;
    }
    public String getId() {
        return id;
    }//获得当前对象的学号，
    public double getComputer_score() {
        return computer_score;
    }//获得当前对象的计算机课程成绩,
    public double getMaths_score() {
        return maths_score;
    }//获得当前对象的数学课程成绩,

    public double getEnglish_score() {
        return english_score;
    }//获得当前对象的英语课程成绩,

    public void setId(String id) {
        this.id = id;
    }// 设置当前对象的id值,

    public void setComputer_score(double computer_score) {
        this.computer_score = computer_score;
    }//设置当前对象的Computer_score值,

    public void setEnglish_score(double english_score) {
        this.english_score = english_score;
    }//设置当前对象的English_score值,

    public void setMaths_score(double maths_score) {
        this.maths_score = maths_score;
    }//设置当前对象的Maths_score值,

    public double getTotalScore() {
        return computer_score + maths_score + english_score;
    }// 计算Computer_score, Maths_score 和English_score 三门课的总成绩。

    public double getAveScore() {
        return getTotalScore() / 3;
    }// 计算Computer_score, Maths_score 和English_score 三门课的平均成绩。

    double sum() {
        return (this.a1 + this.a2 + this.a3);
    }
    public String toString() {
        return "名次：" + this.mingci + " 学号：" + this.xuehao + " 年龄： " + this.age + "  " + this.name + " " + this.a1 + " " +
                this.a2 + " " + this.a3 + " 总分:" + this.sum();
    }

    class Undergraduate extends Student {
        private String classID;

        public Undergraduate(String id, String name, char sex, int age, String classID) {
            super(id, name, sex, age);
            this.classID = classID;
        }

        public String getClassID() {
            return classID;
        }

        public void setClassID(String classID) {
            this.classID = classID;
        }
    }
}

---

测试代码

 * task2
 *
 * @author 20175204
 * @date 2019/5/5
 */
import junit.framework.TestCase;
public class StudentTest extends TestCase {
    public static void main(String[] args) {
        Student[] student = new Student[5];
        student[0] = new Student(20175204, "zyz",20 ,99, 98, 95);
        student[1] = new Student(20175205, "hy",19 ,87, 72, 93);
        student[2] = new Student(20175206, "ldc", 20,88, 73, 91);
        student[3] = new Student(20175207, "ln", 20,99, 94, 56);
        student[4] = new Student(20175208, "zjh",20 ,100, 100, 100);
        Student temp; //排序使用的临时对象
        //按sum排序
        for (int i = 0; i < student.length; i++) {
            for (int j = i+1; j < student.length; j++) {
                if(student[j].sum() > student[i].sum()){
                    temp = student[i];
                    student[i] = student[j];
                    student[j] = temp;
                }
            }
        }
        int mingci = 1;//名次

        for (int i = 0; i < student.length-1; i++) {
            int n = checkContinue(student, student[i].sum());
            if (n == 1) {
                student[i].mingci = mingci++;
            }else {
                //总分相同，名次相同
                for (int j = 0; j < n; j++) {
                    student[i+j].mingci = mingci;
                }
                mingci++;
                i = i + n -1;//连续n个相同的总分，排名一样
            }
        }
        student[student.length-1].mingci = mingci;
        for (int i = 0; i < student.length; i++) {
            System.out.println(student[i]) ;
        }
    }


    //判断是否连续
    public static int checkContinue(Student[] student,double sum){
        int count = 0 ;//统计多少个连续相同的sum
        for (int i = 0; i < student.length; i++) {
            if(student[i].sum() == sum){
                count++;
            }
        }
        return count;
    }

}

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截图