package shuzuxu;import java.io.BufferedReader;
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.io.InputStreamReader;
import java.io.OutputStream;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.*;
public class shuzu {public static void main(String[] args) throws Exception{File f = new File("hello.txt");judeFileExists(f);//判断文件是否存在//用FileOutputSteam包装文件，并设置文件可追加OutputStream out = new FileOutputStream(f,true);Scanner in=new Scanner(System.in);System.out.println("请输入产生随机数的数量：");String nums;int n;while(true)//判断输入是否为整数
                {try{nums=in.next() ;n=Integer.parseInt(nums) ;break ;}catch(Exception e){System.out.println("只能输入整数") ;}}for(int i=0;i<n;i++){java.util.Random r=new java.util.Random();String s=Integer.toString(r.nextInt());out.write(s.getBytes()); //向文件中写入数据out.write('\r'); // \r\n表示换行out.write('\n'); }List list = new ArrayList();BufferedReader bw = new BufferedReader(new FileReader(f));String line = null;//因为不知道有几行数据，所以先存入list集合中while((line = bw.readLine()) != null){list.add(line);}//bw.close();int a=list.size();String[] li=new String[a];for(int i=0;i<list.size();i++){li[i]=(String) list.get(i);System.out.println(li[i]);}BigInteger maxsum = new BigInteger("0");BigInteger maxstart = new BigInteger("0");//用于判断子数组是否小于0BigInteger x = new BigInteger("0");maxsum = new BigInteger(li[0]);BigInteger y;for(int i = 0;i < list.size();i++){if (maxstart.compareTo(x)!=1) {//忽略掉和为负数和0的子数组maxstart = new BigInteger(li[i]);}else {y= new BigInteger(li[i]);BigInteger v=maxstart.add(y);maxstart=v;}if (maxsum.compareTo(maxstart)<0) {maxsum = maxstart;}}System.out.println("最大值为：" + maxsum);FileWriter fileWriter =new FileWriter(f);fileWriter.flush();fileWriter.close();String line1 = null;if((line1 = bw.readLine()) == null){System.out.println("文件清空成功");;}}public static void judeFileExists(File file) {//判断文件是否存在if (file.exists()) {System.out.println("file exists");} else {System.out.println("file not exists, create it ...");try {file.createNewFile();} catch (IOException e) {// TODO Auto-generated catch block
                         e.printStackTrace();}}}
}