题目要求：

代码：

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Student.java:

public class Student {private long id;//学号
    private String name;//姓名
    private double math;//应用数学成绩
    private double English;//大学英语成绩
    private double Java;//java成绩
    private double computer;//计算机应用基础
    private double average;    //平均分
    private int n;  //总人数
    public double getAverage() {return average;
    }

    public void setAverage(double average) {this.average = average;
    }

    public Student(int n,long id, String name, double math, double english, double java, double computer, double average) {this.n = n;
    	this.id = id;
        this.name = name;
        this.math = math;
        this.English = english;
        this.Java = java;
        this.computer = computer;
        this.average=average;
    }
	public Student() {}

	public int getNum() {return n;
    }

    public void setNum(int n) {this.n = n;
    }
    public long getId() {return id;
    }

    public void setId(long id) {this.id = id;
    }

    public String getName() {return name;
    }

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

    public double getMath() {return math;
    }

    public void setMath(double math) {this.math = math;
    }

    public double getEnglish() {return English;
    }

    public void setEnglish(double English) {this.English = English;
    }

    public double getJava() {return Java;
    }

    public void setJava(double Java) {this.Java = Java;
    }

    public double getComputer() {return computer;
    }

    public void setComputer(double computer) {this.computer = computer;
    }
    public double getAvg(Student student) {return ( (student.getMath() + student.getEnglish() + student.getJava() + student.getComputer())/4);

    }
    public void setAvg(double average) {this.average=average;
    }
}

StudentApplication.java:

public class StudentApplication {public static Scanner scanner = new Scanner(System.in);
    public static ArrayListstudents = new ArrayList<>();
    public static void main(String[] args) {Student student = new Student();
        StudentManage sm=new StudentManage();
        while(true){   int menuSelect=StudentManage.getMenu();
           switch (menuSelect){   case 1://输入学生相关信息
                   sm.addStudent(students);
                   break;
                case 2://2按平均分降序排列
                    sm.sortStudent(students);
                    break;
               case 3:// 3显示所有成绩
                   sm.showAllStudent(students);
                   break;
                case 4: //4输入查询个人成绩
                    sm.searchStudent(students);
                    break;
                case 5://5显示各科平均分，最高分，最低分
                	sm.averageScore(students);
                	break;
                case 6://6退出成绩管理系统
                    System.out.println("即将退出成绩管理系统");
                    System.exit(0);
               default:
                   System.out.println("请重新输入");

                   break;

            }
        }

    }
}

StudentManage.java:

public class StudentManage {private static Scanner sc=new Scanner(System.in);

    //得到菜单
    public static int getMenu(){System.out.println("----------学生成绩管理系统----------");
        System.out.println("          1输入学生相关信息");
        System.out.println("          2按平均分降序排列");
        System.out.println("          3显示所有成绩");
        System.out.println("          4输入查询个人成绩");
        System.out.println("          5显示各科平均分，最高分，最低分");
        System.out.println("          6退出成绩管理系统");
        System.out.println("----------学生成绩管理系统----------");
        System.out.println("请选择菜单：");
        int select=StudentManage.sc.nextInt();
        return select;
    }
    //添加学生
    public   void addStudent(ArrayListstudents){Student student=new Student();
        System.out.println("请输入学生的学号");
        student.setId(sc.nextLong());
        System.out.println("请输入学生的姓名");
        student.setName(sc.next());
        System.out.println("请输入学生的应用数学成绩");
        student.setMath(sc.nextDouble());
        System.out.println("请输入学生的大学英语成绩");
        student.setEnglish(sc.nextDouble());
        System.out.println("请输入学生的java程序设计成绩");
        student.setJava(sc.nextDouble());
        System.out.println("请输入学生的计算机应用基础成绩");
        student.setComputer(sc.nextDouble());
        double avg = student.getAvg(student);
        student.setAverage(avg);
        students.add(student);
        //        提示信息
        System.out.println("添加成功");
    }
    //查询学生
    public void searchStudent(ArrayListstudents){if (students.size() == 0) {System.out.println("当前无数据，请添加后重试");
        } else {System.out.println("请输入要查找学生的学号：");
            long id = sc.nextLong();
            int flag = -1;
            Student student = new Student();
            //        查找对应学号，找到就退出
            for (int i = 0; i< students.size(); i++) {student = students.get(i);
                if (student.getId() == id) {flag = i;
                    break;
                }
            }

            if (flag == -1) {System.out.println("未找到对应学号的学生，请确认后重新输入！");
            } else {System.out.println("对应学号的学生成绩如下：");
                System.out.println("学号\t\t\t姓名\t\t数学\t\t英语\t\tJava\t\tcomputer\t\t平均分\t\t");
                System.out.format("%d\t%s\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\n", student.getId(), student.getName(), student.getMath(), student.getEnglish(), student.getJava(),student.getComputer(), student.getAvg(student));
                System.out.println("查找信息成功！");
            }
        }
    }
    //按平均分排降序
    public void sortStudent(ArrayListstudents){if (students.isEmpty()) {System.out.println("当前无数据，请添加后重试");
        } else {for (int i = 0; i< students.size() - 1; i++) {if (students.get(i).getAvg(students.get(i))< students.get(i + 1).getAvg(students.get(i + 1))) {Student tmp = students.get(i);
                    students.set(i, students.get(i + 1));
                    students.set(i + 1, tmp);
                }
            }

            System.out.println("排序后的学生成绩");
            System.out.println("学号\t\t姓名\t\t数学\t\t英语\t\tJava\t\t计算机\t\t平均分");
            for (Student student : students) {System.out.format("%d\t%s\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t\n",  student.getId(), student.getName(), student.getMath(), student.getEnglish(),  student.getJava() ,student.getComputer(), student.getAvg(student));
            }
        }
    }
    //显示所有成绩
    public void showAllStudent(ArrayListstudents){if (students.isEmpty()) {System.out.println("当前无数据，请先添加数据");
        } else {System.out.println("----------所有学生成绩如下----------");
            System.out.println("学号\t\t姓名\t\t数学\t\t英语\t\tJava\t\t计算机\t\t平均分");
            for (Student student : students) {System.out.format("%d\t%s\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\n", student.getId(), student.getName(), student.getMath(), student.getEnglish(), student.getJava(),student.getComputer(), student.getAvg(student));
        }
        }
    }
    //各科平均分，最高分，最低分
        public void averageScore(ArrayListstudents){int n = students.size();
        double max1 = 0;
		double min1 = students.get(0).getMath();;
        double sum1 = 0;
        for (int i = 0; i< n; i++) {	sum1 = sum1 + students.get(i).getMath();
        	 if (students.get(i).getMath() >max1) { max1 = students.get(i).getMath();
             }
            if (students.get(i).getMath()< min1) {min1 = students.get(i).getMath();
            }
        	}
        System.out.println("应用数学的平均成绩="+sum1/n+" 最高成绩="+max1+" 最低成绩="+min1);
        
        double max2 = 0;
		double min2 = students.get(0).getEnglish();;
        double sum2 = 0;
        for (int i = 0; i< n; i++) {	sum2 = sum2 + students.get(i).getEnglish();
        	if (students.get(i).getEnglish() >max2) {max2 = students.get(i).getEnglish();
            }
            if (students.get(i).getEnglish()<= min2) {min2 = students.get(i).getEnglish();
            }
        	}
        System.out.println("大学英语的平均成绩="+sum2/n+" 最高成绩="+max2+" 最低成绩="+min2);
        
        double max3 = 0;
		double min3 = students.get(0).getJava();;
        double sum3 = 0;
        for (int i = 0; i< n; i++) {	sum3 = sum3 + students.get(i).getJava();
        	 if (students.get(i).getJava() >max3) { max3 = students.get(i).getJava();
             }
            if (students.get(i).getJava()<= min3) {min3 = students.get(i).getJava();
            }
        	}
        System.out.println("Java的平均成绩="+sum3/n+" 最高成绩="+max3+" 最低成绩="+min3);
        
        double max4 = 0;
		double min4 = students.get(0).getComputer();;
        double sum4 = 0;
        for (int i = 0; i< n; i++) {	sum4 = sum4 + students.get(i).getComputer();
        	 if (students.get(i).getEnglish() >max4) { max4 = students.get(i).getComputer();
             }
            if (students.get(i).getComputer()<= min4) {min4 = students.get(i).getComputer();
            }
        	}
        System.out.println("计算机应用基础的平均成绩="+sum4/n+" 最高成绩="+max4+" 最低成绩="+min4);
        }
}

运行主界面：

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