import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.File;

import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; import java.util.Date; public class FIleIo {

public static void main(String[] args) { try { File file = new File(\"studentName.txt\"); if(!file.exists()){ file.createNewFile(); } BufferedWriter bw = new BufferedWriter(new FileWriter(file)); BufferedReader br = new BufferedReader(new FileReader(\"studentInfo.txt\")); String line; int number = 1; while (( line = br.readLine()) != null) { String[] sc =line.split(\ bw.write(number+sc[0].trim()); bw.newLine(); bw.flush(); number++; } bw.close(); br.close(); java.text.SimpleDateFormat df = new java.text.SimpleDateFormat(\"yyyy-MM-dd HH:mm:ss.SSS\"); String dateTime=df.format(new Date(file.lastModified())); System.out.println(\"文件修改時(shí)間:\"+dateTime);

System.out.println(\"文件的長(zhǎng)度:\"+file.length()); } catch (IOException e) { e.printStackTrace(); } } }

（2）學(xué)生成績(jī)存儲(chǔ)在文件中，每行一個(gè)學(xué)生成績(jī)，形如： 20151201 85 84 91.5 20151202 70 85 65 …

請(qǐng)編程讀入學(xué)生成績(jī)，并計(jì)算各門課程的均值和方差，寫入文件最后 的最后一行，如：

71/10 81.2/11.3 76/15.3長(zhǎng)度及修改時(shí)間。

package test13_2;

import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.File;

import java.io.FileReader; import java.io.FileWriter; import java.io.IOException; public class Score {

public static void main(String[] args) { // TODO 自動(dòng)生成的方法存根 File file = new File(\"student.txt\"); try { BufferedWriter bw = new BufferedWriter(new FileWriter(file)); BufferedReader br = new BufferedReader(new FileReader(file)); String[] str = new String[]{\"20151201 85 84 91.5\70 85 65\ for(int i = 0;iint sum2 = 0; int sum3 = 0; while (( line = br.readLine()) != null) { String[] sc =line.split(\" \"); sc1 += Double.parseDouble(sc[1]); sc2 += Double.parseDouble(sc[2]); sc3 += Double.parseDouble(sc[3]); number++; sum1 += sc1*sc1; sum2 += sc2*sc2; sum3 += sc3*sc3; } BufferedWriter bw1 = new BufferedWriter(new FileWriter(file,true));

bw1.write(sc1/number+\"/\"+Math.sqrt((sum1-sc1*sc1)/number)+\"\\"+sc2/number+\"/\"+Math.sqrt((sum2-sc2*sc2)/number)+\"\\"+sc3/number+\"/\"+Math.sqrt((sum3-sc3*sc3)/number)); bw1.flush(); bw1.close(); br.close(); } catch (IOException e) { e.printStackTrace(); } } }