**这是我到目前为止所做的。这个程序需要我显示学生信息。运行程序时没有错误，但是没有显示等级。 **
import java.io.*;
import java.math.MathContext;
class StudInfo {
public static DataInputStream d = new DataInputStream(System.in);
public static String matricNo[] = new String[100];
public static String name[] = new String[100];
public static int courseWorkMark []= new int[100];
public static int finalExamMark[] = new int [100];
public static String grade[] = new String[100];
public static double mark1;
public static double mark2;
public static int x = 1;
public static String sgrade;
public static int scourseWorkMark;
public static int sfinalExamMark;
//MENU
public static void main(String[] args)throws IOException {
menu();
}
public static void menu()throws IOException {
System.out.println("<<<-- MAIN MENU -->>>");
System.out.println("");
System.out.println("[1] Add\n[2] Edit\n[3] Delete\n[4] Search\n[5] View\n[6] Exit");
System.out.println("");
System.out.print("Select a menu: ");
int m = Integer.parseInt(d.readLine());
switch(m) {
case 1: //ADD DATA
addData();
break;
case 2: //EDIT DATA
editData();
break;
case 3: //DELETE DATA
DeleteData();
break;
case 4: //SEARCH DATA
SearchData();
break;
case 5: //VIEW DATA
viewData();
break;
case 6: //EXIT SYSTEM
break;
default:
break;
}
}
//DELETE
public static void DeleteData()throws IOException {
boolean result = false;
int index = 0;
spacing();
System.out.print("<<<-- DELETE RECORDS -->>>\n\n");
System.out.print("Search Student Matric Number: ");
String smatricNo = d.readLine();
for(int i=1;i<matricNo.length;i++) {
if(matricNo[i] !=null) {
if(smatricNo.equalsIgnoreCase(matricNo[i])) {
result = true;
index = i;
}
}
}
if(result == true) {
System.out.print("Matric: "+matricNo[index].toUpperCase()+ " ");
System.out.print("Name: "+name[index].toUpperCase()+ " ");
System.out.print("Course Work: "+courseWorkMark[index]+ " ");
System.out.print("Final Exam: "+finalExamMark[index]+ " ");
System.out.print("Grade: "+grade[index].toUpperCase()+ " ");
System.out.println("");
System.out.print("Are you sure to save this record?[y]-y/[n]-no: ");
String Ques = d.readLine();
if(Ques.equalsIgnoreCase("y")) {
matricNo[index] = null;
name[index] = null;
courseWorkMark[index] = 0;
finalExamMark[index] = 0;
grade[index] = null;
for(int j=index+1;j<matricNo.length;j++)
{
matricNo[j-1] = matricNo[j];
name[j-1] = name[j];
courseWorkMark[j-1] = courseWorkMark[j];
finalExamMark[j-1] = finalExamMark[j];
grade[j-1] = grade[j];
}
System.out.println("Record succesfully deleted!");
System.out.println("\n\n<Press Enter>");
String Ques1 = d.readLine();
spacing();
menu();
} else{
spacing();
menu();
}
} else{
System.out.print("Matric Number not found!");
System.out.println("\n\n<Press Enter>");
String Ques = d.readLine();
spacing();
menu();
}
}
//SEARCH
public static void SearchData()throws IOException {
boolean result = false;
int index=0;
spacing();
System.out.print("<<<-- SEARCH DATA -->>>\n\n");
System.out.print("Search Student Matric Number: ");
String smatricNo = d.readLine();
for(int i=1;i<matricNo.length;i++) {
if(matricNo[i] !=null) {
if(smatricNo.equalsIgnoreCase(matricNo[i])) {
result = true;
index = i;
}
}
}
if(result==true) {
System.out.print("Matric: " + matricNo[index].toUpperCase() + " ");
System.out.print("Name: " + name[index].toUpperCase() + " ");
System.out.print("Course Work: " + courseWorkMark[index] + " ");
System.out.print("Final Exam: " + finalExamMark[index] + " ");
System.out.print("Grade: " + grade[index].toUpperCase() + " ");
System.out.println("");
System.out.println("\n\n<Press Enter>");
String Ques = d.readLine();
spacing();
menu();
}else {
System.out.print("Matric Number not found!");
System.out.println("\n\n<Press Enter>");
String Ques = d.readLine();
spacing();
menu();
}
}
//ADD
public static void addData()throws IOException {
spacing();
System.out.print("<<<-- ADD DATA -->>>\n\n");
System.out.print("Student Matric Number: ");
String smatricNo = d.readLine();
System.out.print("Student Name: ");
String sname = d.readLine();
System.out.print("Course Work: ");
scourseWorkMark = Integer.parseInt(d.readLine());
System.out.print("Final Exam: ");
sfinalExamMark = Integer.parseInt(d.readLine());
Calculate();
System.out.print("Grade: " + sgrade);
String sgrade = d.readLine();
System.out.print("Are you sure to save this record?[y]-y/[n]-no: ");
String Ques = d.readLine();
if(Ques.equalsIgnoreCase("y")) {
matricNo[x] = smatricNo;
name[x] = sname;
courseWorkMark[x] = scourseWorkMark;
finalExamMark[x] = sfinalExamMark;
grade[x] = sgrade;
x++;
spacing();
menu();
}else if(Ques.equalsIgnoreCase("n")) {
spacing();
menu();
}
}
public static void spacing() {
System.out.print("\n\n\n");
}
//VIEW
public static void viewData()throws IOException {
boolean center = false;
spacing();
System.out.print("<<<-- VIEW DATA -->>>\n\n");
for(int i=1;i<matricNo.length;i++) {
if(matricNo[i] != null) {
System.out.print("Matric Number: " + matricNo[i].toUpperCase()+ " ");
System.out.print("Name: " + name[i].toUpperCase()+ " ");
System.out.print("Course Work: " + courseWorkMark[i]+ " ");
System.out.print("Final Exam: " + finalExamMark[i]+ " ");
System.out.print("Grade: " + grade[i].toUpperCase()+ " ");
System.out.println("");
center=true;
}
}
if(center == false) {
System.out.print("\nEMPTY DATABASE. NO RECORDS FOUND!");
}
System.out.println("\n\n<Press Enter>");
String Ques = d.readLine();
spacing();
menu();
}
//EDIT
public static void editData()throws IOException {
boolean result = false;
int index=0;
spacing();
System.out.print("<<<-- EDIT DATA -->>>\n\n");
System.out.print("Search Matric Number: ");
String smatricNo = d.readLine();
for(int i=1;i<matricNo.length;i++) {
if(matricNo[i] !=null) {
if(smatricNo.equalsIgnoreCase(matricNo[i])) {
result = true;
index = i;
}
}
}
if(result == true) {
System.out.print(matricNo[index] + " " +name[index]+ " " +courseWorkMark[index]+ " " +finalExamMark[index]+ " " +grade[index]+ " \n\n");
System.out.print("Student Matric Number: ");
String smatricNoedit = d.readLine();
System.out.print("Student Name: ");
String snameedit = d.readLine();
System.out.print("Course Work: ");
scourseWorkMark = Integer.parseInt(d.readLine());
System.out.print("Final Exam: ");
sfinalExamMark = Integer.parseInt(d.readLine());
Calculate();
System.out.print("Grade: " + sgrade);
String sgrade = d.readLine();
System.out.print("Are you sure to update this record?[y]-y/[n]-no: ");
String Ques = d.readLine();
if(Ques.equalsIgnoreCase("y")) {
matricNo[index] = smatricNoedit;
name[index] = snameedit;
courseWorkMark[index] = scourseWorkMark;
finalExamMark[index] = sfinalExamMark;
grade[index] = sgrade;
spacing();
menu();
}
else if(Ques.equalsIgnoreCase("n"))
{
spacing();
menu();
}
}else {
System.out.print("Matric Number not found!");
System.out.println("\n\n<Press Enter>");
String Ques = d.readLine();
spacing();
menu();
}
}
//CALCULATION PART
public static String Calculate()
{
double mark1 = scourseWorkMark * 60 / 100;
double mark2 = sfinalExamMark * 40 / 100;
double totalMark = mark1 + mark2;
if (totalMark >= 90)
{
sgrade = "A+";
}
else if (totalMark >= 80)
{
sgrade = "A";
}
else if (totalMark >= 70)
{
sgrade = "A-";
}
else if (totalMark >= 65)
{
sgrade = "B+";
}
else if (totalMark >= 60)
{
sgrade = "B";
}
else if (totalMark >= 55)
{
sgrade = "C+";
}
else if (totalMark >= 50)
{
sgrade = "C";
}
else if (totalMark >= 45)
{
sgrade = "D";
}
else if (totalMark >= 40)
{
sgrade = "E";
}
else
{
sgrade = "F";
}
return;
}
}
为什么不能显示成绩？
答案 0 :(得分：1)
在public static String Calculate()函数中，您需要返回return sgrade;，目前，您没有返回任何对象，但该方法要求返回string。
此外，从第199行（在addData函数中）删除String sgrade = d.readLine();。这会导致问题，因为您正在定义一个与类变量同名的新变量，而不指定在接下来的几行中使用哪一个。
当我解决这个问题时，输出结果如下：
＆lt;＆lt;＆lt; - 主菜单 - ＆gt;＆gt;＆gt;
[1]添加[2]编辑[3]删除[4]搜索[5]查看[6]退出
选择一个菜单：1
＆lt;＆lt;＆lt; - ADD DATA - ＆gt;＆gt;＆gt;
学生基础编号：1
学生姓名：Jake Chasan
课程作业：100
期末考试：100年级：A +
＆lt;＆lt;＆lt; - 查看数据 - ＆gt;＆gt;＆gt;
Matric Number：1姓名：JAKE课程作业：100
期末考试：100年级：A +