java空指针异常问题 程序运行空指针异常

Question

//这个是学生类
public class Student {
private int on;
private String name;
private int age;
private int java;
private int c;
private int html;
private int sql;
private int sum;
private int avg;
Student(){
}
public int getOn() {
return on;
}
public void setOn(int on) {
this.on = on;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public int getJava() {
return java;
}
public void setJava(int java) {
this.java = java;
}
public int getC() {
return c;
}
public void setC(int c) {
this.c = c;
}
public int getHtml() {
return html;
}
public void setHtml(int html) {
this.html = html;
}
public int getSql() {
return sql;
}
public void setSql(int sql) {
this.sql = sql;
}
public int getSum() {
return sum;
}
public void setSum() {
this.sum = this.java+this.c+this.sql+this.html;
}
public int getAvg() {
return avg;
}
public void setAvg() {
this.avg = this.sum/4;
}
public String toString(){
String msg="\t"+this.on+"\t"+this.name+"\t"+this.age+"\t"+this.java
+"\t"+this.c+"\t"+this.html+"\t"+this.sql+"\t"+this.sum+"\t"
+this.age;
return msg;
}
}

public class Admin {//管理学生类
Student[] stuArr=new Student[10];
public void addStudent(String name,int age,int renShu,int i){
stuArr=new Student[renShu];
stuArr[i].setName(name);
stuArr[i].setAge(age);
}
public String showStudent(){
String show="";
for(int i=0;i<stuArr.length;i++){
show=stuArr[i].toString();
}
return show;
}
}

import java.util.*;

public class Test {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner in=new Scanner(System.in);
    Student student=new Student();
    System.out.println("------请输入学生人数------");
    int studentNum=in.nextInt();
    Student[] stuArr=new Student[studentNum];
    Admin admin=new Admin();
    int c=0;
    do{
        System.out.println("请选择你要执行的功能:");
        System.out.println("10:添加一个学生");
        System.out.println("11:查找一个学生");
        System.out.println("12:根据学生编号跟新学生信息");
        System.out.println("13:根据学生编号删除学生");
        System.out.println("14:根据编号输入学生各门成绩");
        System.out.println("15:根据某门成绩进行排序");
        System.out.println("16:根据总分进行排序");
        System.out.println("99:退出系统");
        c=in.nextInt();
        if(c==10){
            System.out.println("请输入学生姓名:");
            String name=in.next();
            System.out.println("请输入学生年龄:");
            int age=in.nextInt();
            int i=0;
            admin.addStudent(name, age, studentNum, i);
            System.out.println("\t编号\t姓名\t年龄\tjava\tc\thtml\tsql\t总分\t平均分");
            System.out.println(admin.showStudent());
            i++;
        }
    }while(c!=99);
}

}

Answer 1

public void addStudent(String name,int age,int renShu,int i){
stuArr=new Student[renShu];
stuArr[i].setName(name);
stuArr[i].setAge(age);
}

这个不对
首先，根据你调用的代码
admin.addStudent(name, age, studentNum, i);
你不应该每调用一次addStudent就来一个stuArr=new Student[renShu];
其次
stuArr[i].setName(name);
前面应该加上
stuArr[i] = new Student();