static void sort(){ //按照成绩排序 int [][]grade = new int[students.size()][2]; for (int i = 0; i < students.size(); i++) { final Student student = students.get(i); grade[i][0] = student.getGrade(); grade[i][1] = i; } for (int i = 0; i < students.size(); i++) { for (int j = 1; j < students.size() - i; j++) { if (grade[j - 1][0] > grade[j][0]){ int a = grade[j][0]; grade[j][0] = grade[j - 1][0]; grade[j - 1][0] = a; int c = grade[j][1]; grade[j][1] = grade[j - 1][1]; grade[j - 1][1] = c; } } }

这段代码是用来对一个学生列表按照成绩进行排序的。它首先创建了一个二维数组 grade，其中第一列存储学生的成绩，第二列存储学生在原列表中的索引。然后使用冒泡排序算法对 grade 数组进行排序，排序时比较的是 grade 数组的第一列（即学生的成绩）。最终，按照排好序的 grade 数组的第二列，重新排列原学生列表。

相关问题

import java.util.List; import java.util.ArrayList; public class paixubiancheng3 { public static void main(String[] args) { StudentClass sClass = new StudentClass(); sClass.createClass(); System.out.println("Original Order:"); System.out.println(sClass.output()); sClass.sort(); System.out.println("Sorted Order:"); System.out.println(sClass.output()); } } class Student{ private String name; private double grade; private int age; public Student(String name,int age,double grade){ this.name = name; this.age = age; this.grade = grade; } public void setname(){ this.name = name; } public void setgrade(){ this.grade = grade; } public void setage(){ this.age = age; } public String getname(){ return name; } public double getgrade(){ return grade; } public int getage(){ return age; } } class StudentClass{ private int size; private List<Student> stuList; public StudentClass(){ size = 0; stuList = null; } public void createClass(){ String names[] = {"Tom","Jerry","Snoopy","Mary","Rose"}; double grades[] = {67,78.5,98,76.5,90}; int ages[] = {17,18,18,19,17}; size = names.length; stuList = new ArrayList<Student>(); Student temp; for (int i = 0; i<size ;i++ ) { temp = new Student(names[i],ages[i],grades[i]); stuList.add(temp); } } public void sort(){ Student temp; for(int i=0;i<size;i++){ for(int j=1;j<size;j++){ if(stuList.get(j-1).getage()>stuList.get(j).getage()){ temp=stuList.get(j-1); stuList.set(j-1,stuList.get(j)); stuList.set(j,temp); } else if (stuList.get(j-1).getage()=stuList.get(j).getage()){ if(stuList.get(j-1).getname().compareTo(stuList.get(j).getname())>0){ temp=stuList.get(j-1); stuList.set(j-1,stuList.get(j)); stuList.set(j,temp); } } else{} } } } public String output(){ StringBuilder studentInfo = new StringBuilder(); for(Student stu : stuList){ studentInfo.append("Age: "+stu.getage()+"\tName: "+stu.getname()+"\r\n"); } studentInfo.append("total: "+size+" students\n"); return studentInfo.toString(); } public void add(Student s){ stuList.add(s); size = stuList.size(); } }这段代码有错吗？如果有请修改

有几处错误，以下是修改后的代码：

import java.util.List; 
import java.util.ArrayList; 

public class PaixuBiancheng3 { 

    public static void main(String[] args) { 
        StudentClass sClass = new StudentClass(); 
        sClass.createClass(); 
        System.out.println("Original Order:"); 
        System.out.println(sClass.output()); 
        sClass.sort(); 
        System.out.println("Sorted Order:"); 
        System.out.println(sClass.output()); 
    } 

} 

class Student { 
    private String name; 
    private double grade; 
    private int age; 

    public Student(String name, int age, double grade){ 
        this.name = name; 
        this.age = age; 
        this.grade = grade; 
    } 

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

    public void setGrade(double grade){ 
        this.grade = grade; 
    } 

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

    public String getName(){ 
        return name; 
    } 

    public double getGrade(){ 
        return grade; 
    } 

    public int getAge(){ 
        return age; 
    } 
} 

class StudentClass { 
    private int size; 
    private List<Student> stuList; 

    public StudentClass(){ 
        size = 0; 
        stuList = new ArrayList<Student>(); 
    } 

    public void createClass(){ 
        String names[] = {"Tom","Jerry","Snoopy","Mary","Rose"}; 
        double grades[] = {67,78.5,98,76.5,90}; 
        int ages[] = {17,18,18,19,17}; 
        size = names.length; 
        Student temp; 
        for (int i = 0; i<size ;i++ ) { 
            temp = new Student(names[i],ages[i],grades[i]); 
            stuList.add(temp); 
        } 
    } 

    public void sort(){ 
        Student temp; 
        for(int i=0;i<size;i++){ 
            for(int j=1;j<size-i;j++){ 
                if(stuList.get(j-1).getAge()>stuList.get(j).getAge()){ 
                    temp=stuList.get(j-1); 
                    stuList.set(j-1,stuList.get(j)); 
                    stuList.set(j,temp); 
                } else if (stuList.get(j-1).getAge()==stuList.get(j).getAge() 
                           && stuList.get(j-1).getName().compareTo(stuList.get(j).getName())>0){ 
                    temp=stuList.get(j-1); 
                    stuList.set(j-1,stuList.get(j)); 
                    stuList.set(j,temp); 
                } 
            } 
        } 
    } 

    public String output(){ 
        StringBuilder studentInfo = new StringBuilder(); 
        for(Student stu : stuList){ 
            studentInfo.append("Age: "+stu.getAge()+"\tName: "+stu.getName()+"\r\n"); 
        } 
        studentInfo.append("total: "+size+" students\n"); 
        return studentInfo.toString(); 
    } 

    public void add(Student s){ 
        stuList.add(s); 
        size = stuList.size(); 
    } 
}

主要的修改有：

1. 类名 PaixuBiancheng3 首字母应该大写。
2. Student 类中的 setter 方法没有传入参数。
3. StudentClass 类中创建 List 对象时没有初始化，应该改为 `stuList = new ArrayList<Student>();`。
4. sort 方法中的比较条件有误，应该使用 `>` 或 `<` 进行比较。
5. sort 方法中比较年龄相同的情况下，应该再比较姓名的字典序。

4. Collections (1)改写Student类，增加int grade属性。 (2)随机生成100个Student对象放入students数组。 (3)将students数组转换成studentList(List类型)。 (4)使用Collections.sort对student的成绩进行排序。 (5)使用Collections的min和max方法找到成绩最高的和成绩最低学生。 (6)使用Collections的binarySearch查找成绩等于60的学生。 (7)编写方法从studentList找出grade小于60的学生，放入otherList。 (8)使用List的removeAll方法，从studentList中移除otherList。 (9)使用Collections的shuffle方法，打乱studentList中学生排列的顺序。 (10)将studentList转换为数组。

1. 改写Student类，增加int grade属性。

public class Student {
    private String name;
    private int age;
    private int grade;

    public Student(String name, int age, int grade) {
        this.name = name;
        this.age = age;
        this.grade = grade;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public int getGrade() {
        return grade;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", grade=" + grade +
                '}';
    }
}

2. 随机生成100个Student对象放入students数组。

import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }
    }
}

3. 将students数组转换成studentList(List类型)。

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }

        List<Student> studentList = new ArrayList<>();
        for (Student student : students) {
            studentList.add(student);
        }
    }
}

4. 使用Collections.sort对student的成绩进行排序。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }

        List<Student> studentList = new ArrayList<>();
        for (Student student : students) {
            studentList.add(student);
        }

        Collections.sort(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade());
    }
}

5. 使用Collections的min和max方法找到成绩最高的和成绩最低学生。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }

        List<Student> studentList = new ArrayList<>();
        for (Student student : students) {
            studentList.add(student);
        }

        Collections.sort(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade());

        System.out.println("最高成绩学生：" + Collections.max(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade()));
        System.out.println("最低成绩学生：" + Collections.min(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade()));
    }
}

6. 使用Collections的binarySearch查找成绩等于60的学生。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }

        List<Student> studentList = new ArrayList<>();
        for (Student student : students) {
            studentList.add(student);
        }

        Collections.sort(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade());

        int index = Collections.binarySearch(studentList, new Student("", 0, 60), (s1, s2) -> s1.getGrade() - s2.getGrade());

        if (index >= 0) {
            System.out.println("成绩等于60的学生：" + studentList.get(index));
        } else {
            System.out.println("没有成绩等于60的学生");
        }
    }
}

7. 编写方法从studentList找出grade小于60的学生，放入otherList。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }

        List<Student> studentList = new ArrayList<>();
        for (Student student : students) {
            studentList.add(student);
        }

        Collections.sort(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade());

        List<Student> otherList = new ArrayList<>();
        for (Student student : studentList) {
            if (student.getGrade() < 60) {
                otherList.add(student);
            }
        }
    }
}

8. 使用List的removeAll方法，从studentList中移除otherList。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }

        List<Student> studentList = new ArrayList<>();
        for (Student student : students) {
            studentList.add(student);
        }

        Collections.sort(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade());

        List<Student> otherList = new ArrayList<>();
        for (Student student : studentList) {
            if (student.getGrade() < 60) {
                otherList.add(student);
            }
        }

        studentList.removeAll(otherList);
    }
}

9. 使用Collections的shuffle方法，打乱studentList中学生排列的顺序。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }

        List<Student> studentList = new ArrayList<>();
        for (Student student : students) {
            studentList.add(student);
        }

        Collections.sort(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade());

        List<Student> otherList = new ArrayList<>();
        for (Student student : studentList) {
            if (student.getGrade() < 60) {
                otherList.add(student);
            }
        }

        studentList.removeAll(otherList);

        Collections.shuffle(studentList);
    }
}

10. 将studentList转换为数组。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Main {
    public static void main(String[] args) {
        Random random = new Random();
        Student[] students = new Student[100];
        for (int i = 0; i < students.length; i++) {
            students[i] = new Student("Student" + i, random.nextInt(10) + 15, random.nextInt(101));
        }

        List<Student> studentList = new ArrayList<>();
        for (Student student : students) {
            studentList.add(student);
        }

        Collections.sort(studentList, (s1, s2) -> s1.getGrade() - s2.getGrade());

        List<Student> otherList = new ArrayList<>();
        for (Student student : studentList) {
            if (student.getGrade() < 60) {
                otherList.add(student);
            }
        }

        studentList.removeAll(otherList);

        Collections.shuffle(studentList);

        Student[] studentArray = studentList.toArray(new Student[0]);
    }
}