先生成你需要的文件，然后再读入文件，并计算结果。

import java.io.File;

import java.util.*;

import java.util.Random;

import java.io.BufferedReader;

import java.io.FileWriter;

import java.io.FileReader;

import java.io.IOException;

import java.io.FileNotFoundException;

public class Demo {

x09public static void writefile() throws IOException {

x09x09FileWriter fileWriter=new FileWriter("c:\fileIn.txt");

x09x09Random ran1=new Random();

x09x09for(int i = 0; i < 20;i++) {

x09x09x09int ww = ran1.nextInt()%150;

System.out.println(ww);

x09x09x09fileWriter.write(String.valueOf(ww)+"n");

}

x09x09fileWriter.flush();

x09x09fileWriter.close();

x09}

x09

x09public static void readfile() throws IOException {

x09x09//FileReader fileReader=new FileReader("c:\fileIn.txt");

x09x09File file = new File("C:/fileIn.txt");

x09x09BufferedReader reader = null;

x09x09String tempString = null;

x09x09//Arraylist new_input = new

x09x09ArrayList new_input = new ArrayList();

x09x09int line = 0;

x09x09int less_than = 0;

x09x09int middle_num = 0;

x09x09int bigger_num =0;

x09x09int sum =0;

x09x09int max =0;

x09x09int min = 0;

x09x09try {

x09x09x09reader = new BufferedReader(new FileReader(file));

x09x09x09while ((tempString = reader.readLine()) != null) {

x09x09x09x09System.out.println("Line"+ line + ":" +tempString);

x09x09x09x09int aa = Integer.parseInt(tempString);

x09x09x09x09new_input.add(aa);

x09x09x09x09System.out.println("Line"+ line + ":" +aa);

x09x09x09x09line ++ ;

x09x09x09}

x09x09x09reader.close();

x09x09} catch (FileNotFoundException e) {

x09x09x09// TODO Auto-generated catch block

x09x09x09e.printStackTrace();

x09x09}

x09x09//next is to process the lines

x09x09line = 0;

x09x09for(int x:new_input) {

x09x09x09sum +=x;

x09x09x09if (line ==0) { max = x; min =x; }

x09x09x09if (x > max) max =x;

x09x09x09if (x < min) min =x;

x09x09x09line++;

x09x09}

x09x09System.out.println("sum is : " +sum);

x09x09System.out.println("max is : " +max);

x09x09System.out.println("min is : " +min);

x09x09System.out.println("num is : " +line);

x09x09System.out.println("Average is : " +sum/line);

x09x09//next is to write file

x09x09FileWriter fileWriter=new FileWriter("c:\fileOut.txt");

x09x09float aaaa = (float)sum/line;

x09x09fileWriter.write("average is "+aaaa+ "n");

x09x09fileWriter.write("max is "+max+ "n");

x09x09fileWriter.write("min is "+min+ "n");

x09x09fileWriter.flush();

x09x09fileWriter.close();

x09}x09

public static void main(String[] args) throws Exception {

x09x09Demo demo1 = new Demo();

x09x09demo1.writefile();

x09x09demo1.readfile();

}

}