Java程序设计教程（第三版） 雍俊海 7.3 答案/代码

哎，为了期末考试，每个都试了一下，也不知道对不对、、、

题目：

编写一个程序。要求输入5个学生的成绩（从0到100的整数），并将这5个数保存到文件“data.txt” 中。

然后再编写一个程序，从文件“data.txt” 中读取这5个学生的成绩，

计算并输出它们的平均数，然后再按从大到小的顺序输出5个学生的成绩

代码：

Scanner+FileOutputStream+FileInputStream

import java.io.*;import java.util.*;public class test1_7 {//Scanner+FileOutputStream+FileInputStreampublic static void main(String args[]) throws IOException{int cur_Grade;Scanner sc = new Scanner(System.in);try {OutputStream fos = new FileOutputStream(new File("data.txt"));for(int i=0;i<5;i++){cur_Grade = sc.nextInt();fos.write(cur_Grade);}fos.close();} catch (FileNotFoundException e) {e.printStackTrace();}sc.close();int[] Grades = new int[10];int i =0;double sum = 0;int readnum;InputStream fis = new FileInputStream(new File("data.txt"));while((readnum = fis.read())!=-1){Grades[i++] = readnum;}fis.close();Arrays.sort(Grades,0,5);for(i=0;i<5;i++){sum += Grades[i];System.out.print(Grades[i]+"　");}System.out.println("\n平均数为："+sum/5);}}

DataOutputStream+BufferedReader

import java.io.*;import java.util.*;public class test1_7 {//DataOutputStream+BufferedReaderpublic static void main(String args[]){try{DataInputStream d_is = new DataInputStream(System.in);FileOutputStream f_os = new FileOutputStream("data.txt");DataOutputStream d_os = new DataOutputStream(f_os);for(int i=0 ; i<5 ; i++){int n = d_is.readInt();d_os.writeInt(n);}int n = 5;double score[] = new double[5];String line;FileReader fr = new FileReader("data.txt");BufferedReader i_br = new BufferedReader(fr);int row = 0;while((line = i_br.readLine())!=null){score[row++] = Double.parseDouble(line);}i_br.close();fr.close();Arrays.sort(score);for(int i=0 ; i

BufferedReader+BufferedWriter

import java.io.*;import java.util.*;public class test1_7 {//BufferedReader+BufferedWriterpublic static void main(String args[]){try{int n = 5;double score[] = new double[5];String line;InputStreamReader i_sr = new InputStreamReader(System.in);BufferedReader br = new BufferedReader(i_sr);//BufferedWrtier不要写错了，这里是没有File的！FileWriter fw = new FileWriter("file1.txt");BufferedWriter b_fw = new BufferedWriter(fw);System.out.println("请输入学生成绩:");for(int i=0 ; i


PrintStream+BufferedReader


import java.io.*;import java.util.*;public class test1_7 {//PrintStream+BufferedReaderpublic static void main(String args[]){try{Scanner scan = new Scanner(System.in);File file = new File("file2.txt");FileOutputStream f_os = new FileOutputStream(file);PrintStream ps = new PrintStream(f_os);int ch;for( int i=0 ; i<5 ; i++ ){ch = scan.nextInt();ps.println(ch + "");}ps.close();int n = 5;double score[] = new double[5];String line;FileReader fr = new FileReader("file2.txt");BufferedReader i_br = new BufferedReader(fr);int row = 0;while((line = i_br.readLine())!=null){score[row++] = Double.parseDouble(line);}i_br.close();fr.close();Arrays.sort(score);for(int i=0 ; i

有错的话，还望纠正一下，感觉还是很多问题没有解决的