java运行错误
package twenty_one;import java.io.*;
import java.util.*;
public class Nine {
public static void main(String[] args) throws IOException{
Comparator<Student>cmp=Collections.reverseOrder();
Set<Student>stus=StudentInfoTool.getStudent(cmp);
StudentInfoTool.wrToFile(stus);
}
}
class Student implements Comparable<Student>
{
private String name;
private int ma,cn,en;
private int sum;
Student(String name,int ma,int cn,int en)
{
this.name=name;
this.ma=ma;
this.cn=cn;
this.en=en;
sum=ma+cn+en;
}
public int compareTo(Student s)
{
int num=new Integer(this.sum).compareTo(new Integer(s.sum));
if(num==0)
return this.name.compareTo(s.name );
return num;
}
public String getName()
{
return name;
}
public int getSum()
{
return sum;
}
public int hashCode()
{
return name.hashCode()+sum*78;
}
public boolean equals(Object obj)
{
if(!(obj instanceof Student))
throw new ClassCastException("类型不匹配");
Student s=(Student)obj;
return this.name.equals(s.name)&& this.sum==s.sum;
}
public String toString()
{
return "Student["+name+","+ma+","+","+cn+","+en+"]";
}
}
class StudentInfoTool
{
public static Set<Student>getStudent()throws IOException
{
return getStudent(null);
}
public static Set<Student>getStudent(Comparator<Student>cmp)throws IOException
{
BufferedReader bufr=new BufferedReader(new InputStreamReader(System.in));
String line=null;
Set<Student>stus=null;
if(cmp==null)
new TreeSet<Student>();
else
new TreeSet<Student>(cmp);
while((line=bufr.readLine())!=null)
{
if("over".equals(line))
break;
String[] info=line.split(",");
Student stu=new Student(info[0],Integer.parseInt(info[1]),Integer.parseInt(info[2]),Integer.parseInt(info[3]));
stus.add(stu);
}
bufr.close();
return stus;
}
public static void wrToFile(Set<Student>stus)throws IOException
{
BufferedWriter bufw=new BufferedWriter(new FileWriter("D://java//workspace//heima//src//twenty_one//File//stuinfo.txt"));
for(Student stu:stus)
{// bufw.write(stu.getName());//只出现姓名与总成绩。
bufw.write(stu.toString()+"\t");
bufw.write(stu.getSum()+"");
bufw.newLine();
bufw.flush();
}
bufw.close();
}
}
这段代码运行出现：
Exception in thread "main" java.lang.NullPointerException
at twenty_one.StudentInfoTool.getStudent(Nine.java:77)
at twenty_one.Nine.main(Nine.java:7)
这样的错误为什么啊？ java --------------------编程问答-------------------- 空指针，检查下这一行。
twenty_one.StudentInfoTool.getStudent(Nine.java:77) --------------------编程问答-------------------- 该怎么解决啊？ --------------------编程问答--------------------
学会自己debug，用工具定位问题，而不是直接问怎么解决，如果代码是你自己写的，相信你会调。 --------------------编程问答-------------------- 试试，是什么问题 --------------------编程问答-------------------- 给点提示,这段代码是做什么用的啊 --------------------编程问答-------------------- stus.add(stu); stus为空指针。 --------------------编程问答--------------------
支持!
补充：Java , Java SE
