写了一个小的控制台的信息系统，但是其中有问题，看了好久，不知道什么原因，请大神看看
程序代码：package Homework;
import java.util.*;
public class Work9 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
try{
System.out.println("请输入学生的总人数：");
int size = sc.nextInt();
Manage ma = new Manage(size);
ma.addStu(); //问题从这里开始：跳到下面
ma.getGrade();
ma.getStuNumber();
ma.count();
ma.removeStu();
}catch(Exception e){
e.printStackTrace();
}finally{
try{
sc.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
}
class Manage
{
ArrayList<Student> al = null;
public Manage(int size)
{
al = new ArrayList<Student>(size);
}
public void addStu()
{
Scanner sc = new Scanner(System.in);
try{
System.out.println("cuowu isnot here");
for(int i=0; i<al.size(); i++) //for循环就没有被执行这是为什么呢？
{
System.out.println("cuowu isnot here");
System.out.print("请输入第"+(i+1)+"个学生的学号："); //另外想问的就是，若创建了多个Scanner输入流，怎么关闭，当关了一个就会抛出异常的，为什么啊？
String number = sc.nextLine();
System.out.print("请输入第"+(i+1)+"个学生的姓名：");
String name = sc.nextLine();
System.out.print("请输入第"+(i+1)+"个学生的成绩：");
float grade = sc.nextFloat();
System.out.println();
Student st = new Student();
st.setName(name);
st.setNumber(number);
st.setGrade(grade);
al.add(st);
}
}catch(Exception e){
e.printStackTrace();
}
System.out.println();
}
public void getGrade()
{
Scanner sc = new Scanner(System.in);
try{
System.out.println("请输入该学生的学号： ");
String number = sc.nextLine();
for(int i=0; i<al.size(); i++)
{
Student st = al.get(i);
if(st.getNumber().equals(number))
{
System.out.println("该学生的成绩为："+st.getGrade());
}
}
}catch(Exception e){
e.printStackTrace();
}
System.out.println();
}
public void getStuNumber()
{
Scanner sc = new Scanner(System.in);
try{
System.out.println("请输入该学生的成绩： ");
float grade = sc.nextFloat();
for(int i=0; i<al.size(); i++)
{
Student st = al.get(i);
if(st.getGrade()==grade)
{
System.out.println("得到该成绩的学生学号为："+st.getNumber());
}
}
}catch(Exception e){
e.printStackTrace();
}
System.out.println();
}
public void count()
{
int A = 0;
int B = 0;
int C = 0;
int D = 0;
for(int i=0; i<al.size(); i++)
{
Student st = al.get(i);
float grade = st.getGrade();
if(grade>=90)
{
A++;
}
else if(grade>=80 && grade<90)
{
B++;
}
else if(grade>=70 && grade<80)
{
C++;
}
else
{
D++;
}
}
System.out.println("得到优的学生共有== "+A+" ==人");
System.out.println("得到良的学生共有== "+B+" ==人");
System.out.println("得到中的学生共有== "+C+" ==人");
System.out.println("得到差的学生共有== "+D+" ==人");
System.out.println();
}
public void removeStu()
{
Scanner sc = new Scanner(System.in);
try{
System.out.println("请输入想要删除的学生的学号");
String number = sc.nextLine();
for(int i=0; i<al.size(); i++)
{
Student st = al.get(i);
if(st.getNumber() == number)
{
al.remove(i);
break;
}
}
}catch(Exception e){
e.printStackTrace();
}finally{
try{
sc.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
}
class Student
{
private String number;
private String name;
private float grade;
public float getGrade() {
return grade;
}
public void setGrade(float grade) {
this.grade = grade;
}
public String getNumber() {
return number;
}
public void setNumber(String number) {
this.number = number;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
