课堂练习二维数组

1.要求数组从文件读取。

2.如果输入的数组很大，并且有很多大的数字，就会产生比较大的结果（考虑一下数的溢出），请保持你的程序正常输出。

3.另外，如果输入文件的参数有错误，这个程序应该能正确退出，并显示相应的错误。任何输入错误都不能导致你的程序崩溃。

代码：

package shuzu;

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("数组实验文件.txt");
                judeFileExists(f);
                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)
                {
                      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()); 
                    out.write('\r');
                    out.write('\n'); 
                }
                List list = new ArrayList();
                BufferedReader bw = new BufferedReader(new FileReader(f));
                 String line = null;
                   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");
                   BigInteger x = new BigInteger("0");
                    maxsum = new BigInteger(li[0]);
                    BigInteger y;
                    for(int i = 0;i < list.size();i++)
                    {
                        if (maxstart.compareTo(x)!=1) {
                            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) {
                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();
                     }
                 }
         }
}