java如何实现对同一个text文本边写边读

import java.io.*

import java.lang.*

import java.util.Scanner

import java.io.*

import java.lang.*

public class Sy2Student

{

public static void main(String []args)

{

Writer Swriter=null

Scanner s=new Scanner(System.in)

System.out.print("输入学生的人数：")

int Studentpeople=s.nextInt()

String []StudentScore=new String[Studentpeople]

String []StudentName=new String[Studentpeople]

System.out.println("请输入学生的侍瞎姓名和总分")

for(int i=0i<Studentpeoplei++)

{

StudentName[i]=s.next()

StudentScore[i]=s.next()

System.out.println("\n")

}

int []IntStudentScore=new int[Studentpeople]

for(int n=0n<Studentpeoplen++)

{

IntStudentScore[n]=Integer.parseInt(StudentScore[n])

}

int StudentScoreMin=IntStudentScore[0]

int StudentScoreMax=IntStudentScore[0]

for(int m=1m<Studentpeoplem++)

{

int AllScore=IntStudentScore[0]

AllScore+=IntStudentScore[m]

//求最低分

if(StudentScoreMin>IntStudentScore[m])

StudentScoreMin=IntStudentScore[m]

else

StudentScoreMin=StudentScoreMin

}

//求最高分

for(int p=0p<慧贺Studentpeoplep++)

{

if(StudentScoreMax<IntStudentScore[p])

StudentScoreMax=IntStudentScore[p]

else

StudentScoreMax=StudentScoreMax

}

try{

Swriter=new FileWriter("Student.txt")

Swriter.write("学生成绩表单\n")

Swriter.write("姓名前谈派：\t\t总分：\n")

for(int j=0j<Studentpeoplej++)

{

Swriter.write(StudentName[j]+"\t\t")

Swriter.write(StudentScore[j]+"\n")

}

Swriter.write("最高分:"+StudentScoreMax+"\n")

Swriter.write("最低分:"+StudentScoreMin+"\n")

}catch(IOException e){

e.printStackTrace()

}finally{

if(Swriter!=null)

try{

Swriter.close()

}catch(IOException e){}

}

Reader RStudent=null

try{

RStudent=new FileReader("Student.txt")

char []buffer=new char[1024]

int offset

while((offset=RStudent.read(buffer))>0)

System.out.println(new String(buffer,0,offset))

}catch(FileNotFoundException e){

e.printStackTrace()

}catch(IOException e){

e.printStackTrace()

}finally{

if(RStudent!=null)

try{

RStudent.close()

}catch(IOException e){}

}

}

}

你可以参考着个程序 我自己写的

读取文件有三种方式，r, w, a，读，覆盖写， 追加写， new FileReader(file)以读的方式打开了文件，两个马上咐颂拆就以new FileWriter(file)方式衡枣覆盖写文件，文件自然是空白的，之后你readLine读到的樱首是null,即String line是null,然后你要writer.write(line) 即writer.write(null)自然报空指针；

建议，如果边读边写，考虑RandomAccessFile类

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