这是我的学生记录系统代码。我认为它完成了80％。这里的问题是，当我有很多学生并且我更新特定学生（主题和年级）时，更新的元素不会保存在该特定学生上。当我显示所有结果时，更新的值将提供给其他学生。请帮我解决这个问题。顺便说一句，这段代码有2个班级Student和StudentGrade。我希望你能帮我解决这个问题。提前致谢。 :)并提前新年快乐！
public class Student
{
private String IDNumber;
private String firstName;
private String middleName;
private String lastName;
private String degree;
private int yearLevel;
public Student()
{
String IDNum;
String fName;
String mName;
String lName;
String deg;
int level;
}
public Student(String IDNum, String fName, String mName, String lName, String deg,int level )
{
this.IDNumber=IDNum;
this.firstName=fName;
this.middleName=mName;
this.lastName=lName;
this.degree=deg;
this.yearLevel=level;
}
public void setIdNumber(String IDNumber)
{
this.IDNumber = IDNumber;
}
public String getIdNumber()
{
return IDNumber;
}
public void setFirstName(String firstName)
{
this.firstName=firstName;
}
public String getFirstName()
{
return firstName;
}
public void setMiddleName(String middleName)
{
this.middleName=middleName;
}
public String getMiddleName()
{
return middleName;
}
public void setLastName(String lastName)
{
this.lastName=lastName;
}
public String getLastName()
{
return lastName;
}
public void setDegree(String degree)
{
this.degree=degree;
}
public String getDegree()
{
return degree;
}
public void setYearLevel(int yearLevel)
{
this.yearLevel=yearLevel;
}
public int getYearLevel()
{
return yearLevel;
}
}
public class StudentGrade
{
private String IDNumber;
private String subject;
private double grade;
private double average;
public StudentGrade()
{
String IDNum;
String sub;
double grad;
double ave;
}
public StudentGrade(String IDNum,String sub,double grad,double ave)
{
this.IDNumber=IDNum;
this.subject=sub;
this.grade=grad;
this.average=ave;
}
public void setSubject(String subject)
{
this.subject=subject;
}
public String getSubject()
{
return subject;
}
public void setGrade(double grade)
{
this.grade=grade;
}
public double getGrade()
{
return grade;
}
public String getIDNumber()
{
return IDNumber;
}
}
public class StudentGrade
{
private String IDNumber;
private String subject;
private double grade;
private double average;
public StudentGrade()
{
String IDNum;
String sub;
double grad;
double ave;
}
public StudentGrade(String IDNum,String sub,double grad,double ave)
{
this.IDNumber=IDNum;
this.subject=sub;
this.grade=grad;
this.average=ave;
}
public void setSubject(String subject)
{
this.subject=subject;
}
public String getSubject()
{
return subject;
}
public void setGrade(double grade)
{
this.grade=grade;
}
public double getGrade()
{
return grade;
}
public String getIDNumber()
{
return IDNumber;
}
}
import java.util.ArrayList;
import java.util.Scanner;
public class test2 {
static ArrayList<Student> studentList = new ArrayList<Student>();
static ArrayList<StudentGrade> studentLists = new ArrayList<StudentGrade>();
public static void main(String[] args)
{
menu();
}
public static void menu()
{
Scanner in = new Scanner(System.in);
int choice = 0;
System.out.print("*********STUDENT RECORD SYSTEM*********\n\n");
System.out.println("\t MENU ");
System.out.println("[1]ADD STUDENT");
System.out.println("[2]DISPLAY ALL");
System.out.println("[3]DISPLAY SPECIFIC");
System.out.println("[4]UPDATE");
System.out.println("[5]AVERAGE");
System.out.println("[6]EXIT");
System.out.println("?");
choice = in.nextInt();
if (choice == 1)
{
add();
}
else if (choice == 2)
{
displayAll();
}
else if (choice == 3)
{
displaySpecific();
}
else if (choice == 4)
{
update();
}
else if (choice == 5)
{
average();
}
else if( choice == 6)
{
System.exit(0);
}
else
menu();
}
public static void add()
{
Scanner in = new Scanner(System.in);
char ans;
String temp;
int total;
do {
System.out.println("NUMBER OF STUDENTS YOU WANT TO INPUT: ");
total = in.nextInt();
Student[] student = new Student[total];
for (int index = 0; index < student.length; index++) {
student[index] = new Student();
System.out.print("**********STUDENT INFORMATION**********\n\n");
System.out.println("PRESS ENTER");
in.nextLine();
System.out.print("ID NUMBER: ");
student[index].setIdNumber(in.nextLine());
System.out.print("FIRST NAME: ");
student[index].setFirstName(in.nextLine());
System.out.print("MIDDLE NAME: ");
student[index].setMiddleName(in.nextLine());
System.out.print("LAST NAME: ");
student[index].setLastName(in.nextLine());
System.out.print("DEGREE: ");
student[index].setDegree(in.nextLine());
System.out.print("YEAR LEVEL: ");
student[index].setYearLevel(in.nextInt());
studentList.add(student[index]);
}
System.out.print("Would you like to enter in a new student (y/n)? ");
String answer = in.next();
ans = answer.charAt(0);
} while (ans == 'y');
/* // SEARCH and DISPLAY SPECIFIC
String id = new String();
in.nextLine();
System.out.print("Enter ID NUMBER: ");
id = in.nextLine();
for (int j = 0; j < studentList.size(); j++) {
if (id.equals(studentList.get(j).getIdNumber())) {
System.out.printf("STUDENT SEARCHED");
System.out.print("\nID NUMBER: "
+ studentList.get(j).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(j).getFirstName() + " "
+ studentList.get(j).getMiddleName() + " "
+ studentList.get(j).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(j).getDegree() + "-"
+ studentList.get(j).getYearLevel() + "\n\n");
System.out.println();
}
}
// DISPLAY ALL
for (int i = 0; i < studentList.size(); i++) {
System.out.printf("STUDENT[%d]", i + 1);
System.out
.print("\nID NUMBER: " + studentList.get(i).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(i).getFirstName() + " "
+ studentList.get(i).getMiddleName() + " "
+ studentList.get(i).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(i).getDegree() + "-"
+ studentList.get(i).getYearLevel());
System.out.println();
} */
menu();
}
public static void displayAll() {
Scanner in = new Scanner(System.in);
if(studentList.size() == 0)
{
System.out.print("EMPTY lageeeee!!! \nPLEASE INPUT FIRST\n\n");
in.nextLine();
}
else
{
if(studentLists.size() == 0){
System.out.print("************STUDENT RECORD*************");
for (int i = 0; i < studentList.size(); i++) {
System.out.printf("\nSTUDENT[%d]", i + 1);
System.out
.print("\nID NUMBER: " + studentList.get(i).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(i).getFirstName() + " "
+ studentList.get(i).getMiddleName() + " "
+ studentList.get(i).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(i).getDegree() + "-"
+ studentList.get(i).getYearLevel()/* +"\nGrade: "
+ studentLists.get(i).getGrade() */+"\n\n");
}
in.nextLine();
}
else{
System.out.print("************STUDENT RECORD*************");
for (int i = 0; i < studentList.size(); i++)
{
System.out.printf("\nSTUDENT[%d]", i + 1);
System.out
.print("\nID NUMBER: " + studentList.get(i).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(i).getFirstName() + " "
+ studentList.get(i).getMiddleName() + " "
+ studentList.get(i).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(i).getDegree() + "-"
+ studentList.get(i).getYearLevel()+"\n\n");
}
for(int xxx = 0 ; xxx < studentLists.size(); xxx++ )
{
System.out.printf("\nSUBJECT: "
+ studentLists.get(xxx).getSubject()+" Grade: "
+ studentLists.get(xxx).getGrade());
}
in.nextLine();
}
}
menu();
}
public static void displaySpecific() {
Scanner in = new Scanner(System.in);
if(studentList.size() == 0)
{
System.out.print("EMPTY oe!!! KALAGOT!\nPLEASE INPUT FIRST\n");
in.nextLine();
}
else
{
String id = new String();
/* in.nextLine(); */
System.out.print("Enter ID NUMBER: ");
id = in.nextLine();
if(studentLists.size()==0)
{
for (int j = 0; j < studentList.size(); j++)
{
if (id.equals(studentList.get(j).getIdNumber()))
{
System.out.printf("\n*************STUDENT SEARCHED*************");
System.out.print("\nID NUMBER: "
+ studentList.get(j).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(j).getFirstName() + " "
+ studentList.get(j).getMiddleName() + " "
+ studentList.get(j).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(j).getDegree() + "-"
+ studentList.get(j).getYearLevel() + /* "\nGrade: "
+ studentLists.get(j).getGrade()+ */"\n\n");
System.out.println();
in.nextLine();
}
/* else
{
System.out.print("STUDENT DOES NOT EXIST IN THIS WORLD!");
in.nextLine();
} */
}
}
else
{
for (int j = 0; j < studentList.size(); j++)
{
if (id.equals(studentList.get(j).getIdNumber()))
{
System.out.printf("\n*************STUDENT SEARCHED*************");
System.out.print("\nID NUMBER: "
+ studentList.get(j).getIdNumber());
System.out.print("\nFULL NAME: "
+ studentList.get(j).getFirstName() + " "
+ studentList.get(j).getMiddleName() + " "
+ studentList.get(j).getLastName());
System.out.print("\nDEGREE and YEAR: "
+ studentList.get(j).getDegree() + "-"
+ studentList.get(j).getYearLevel() +"\n\n");
System.out.println();
}
}
for(int xxx = 0 ; xxx < studentLists.size(); xxx++ )
{
System.out.printf("\nSUBJECT: "
+ studentLists.get(xxx).getSubject()+" Grade: "
+ studentLists.get(xxx).getGrade());
}
in.nextLine();
}
}
menu();
}
public static void update()
{
Scanner in = new Scanner(System.in);
String idnum = new String();
char answer;
in.nextLine();
System.out.print("Enter ID NUMBER: ");
idnum = in.nextLine();
int total;
for(int x=0;x<studentList.size();x++)
{
if(idnum.equals(studentList.get(x).getIdNumber()))
{
System.out.println("NUMBER OF SUJECTS YOU WANT TO INPUT: ");
total = in.nextInt();
do
{
StudentGrade[] update = new StudentGrade[total];
for(int y = 0;y<update.length;y++)
{
update[y] = new StudentGrade();
in.nextLine();
System.out.print("ENTER SUBJECT: ");
update[y].setSubject(in.nextLine());
System.out.print("ENTER GRADE: ");
update[y].setGrade(in.nextDouble());
studentLists.add(update[y]);
}
System.out.print("Enter another subject and grade? [y/n]");
String ans = in.next();
answer = ans.charAt(0);
}while(answer == 'y');
}
menu();
}
}
public static void average()
{
Scanner in = new Scanner(System.in);
double sum=0;
double average=0;
String ID = new String();
System.out.print("ENTER ID NUMBER: ");
ID = in.nextLine();
for(int xx=0;xx<studentList.size();xx++)
{
if(ID.equals(studentList.get(xx).getIdNumber()))
{
for(int ind=0;ind<studentLists.size();ind++)
{
sum += studentLists.get(ind).getGrade();
average=sum/studentLists.size();
}
System.out.print("ID NUMBER:"+studentList.get(xx).getIdNumber()+"\nNAME: "
+studentList.get(xx).getFirstName()+" "
+studentList.get(xx).getMiddleName()+" "
+studentList.get(xx).getLastName());
System.out.print("\nAVERAGE: "+average+"\n");
in.nextLine();
}
}
menu();
}
}
答案 0 :(得分：0)
首先，我将studentList更改为Map，以便能够直接通过id获取学生，而不是每次都搜索匹配的学生。
对所有学生的收藏的访问是这样的：
for(Map.Entry<String, Student> entry : studentList.entrySet()){
String id = entry.getKey();
Student student = entry.getValue();
// ...
}
第二步，您应该检查更新方法。我看，你是在搜索学生，但是你没有更新这个对象。您在循环结束时使用studentList.add()添加新的。
您已将匹配的学生存储到本地变量中，只需修改此项而不修改学生集合。
答案 1 :(得分：0)
更新功能中有两个读者语句
public static void update()
{
Scanner in = new Scanner(System.in);
String idnum = new String();
char answer;
Scanner in = new Scanner(System.in);
String idnum = new String();
char answer;
in.nextLine();//1
System.out.print("Enter ID NUMBER: ");
idnum = in.nextLine();//2
我认为应该只有一个作为你刚读取的id号，而@Vlad说你在数组列表中添加一个新元素而不是修改现有数据。 您的代码也可以使用
arrayList.set(index i,String replaceElement);// this will help you replace the value at a particular index
最好使用HashMap而不是数组列表，以便在将现有元素放入时使用 地图上的值被覆盖。
static Map <String,Student> studentList = new HashMap<String,Student>();
static Map<String, List<StudentGrade>> studentLists = new HashMap<String, List<StudentGrade>>();
这里的密钥将是学生idNumber