求数组的子数组的最大值（文件存储）

　　这周我们老师布置了在上一周的基础上实现文件的存储以及读取，刚开始我先将文件存储以及相关的程序写出来，通过询问老师发现对于数组空间的定义可以使用变量形式，经过这个方法我完成了对任意大小的数据可以进行储存以及读取，之后有听取其他同学的惊讶能使用biginteger类来实现大数据的存储。

源代码：

package lianxi;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.math.BigInteger;
import java.util.Scanner;

public class App7 {
    public static void main(String[] args) throws IOException 
    {
        Scanner in= new Scanner(System.in);
        //writeFile();
        int hang=gethang();
        String[] num=getnum(hang);
        String[] num2=new String [hang];
        String max="0";
        BigInteger bi,bi2;
        int s;
        boolean f=false;
        for(s=0;s<num.length;s++) {
            if(num[s]==null)break;
            bi=new BigInteger (num[s]);
            if(bi.max(BigInteger.valueOf(0))!=BigInteger.valueOf(0))f=true;
        }
        if(f==true) {
        max=num[0];
        num2[0]=num[0];
        for(int i=1;i<s;i++) {
            //num2[i]=num2[i-1]+num[i];
            bi=new BigInteger (num[i]);
            bi2=new BigInteger (num2[i-1]);
            num2[i]=""+bi2.add(bi);
            if(bi.max(bi2)==bi)max=num2[i];
        }
        for(int i=0,j=0;j<s;) {            //循环减去第一个
            bi=new BigInteger (num2[i]);
            bi2=new BigInteger (num[j]);
            bi=bi.subtract(bi2);
            if(bi.max(bi2)==bi)max=num2[i];
            if(i==s-1) {j++;i=j;}
            else i++;
        }
        }
        else {
            max=num[0];
            num2[0]=num[0];
            for(int i=1;i<s;i++) {
                num2[i]=num2[i-1]+num[i];
                bi=new BigInteger (num[i]);
                bi2=new BigInteger (num[i-1]);
                if(bi.max(bi2)==bi)max=num2[i];
            }
        }
        System.out.println(max);
        //add();
        in.close();
    }
    public static int gethang() {
        int i=0;
        try (FileReader reader = new FileReader("text.txt"); 
                BufferedReader br = new BufferedReader(reader)) 
            { 
            String line;  
            while ((line = br.readLine()) != null) {
                i++;
             }
            } 
            catch (IOException e)
            { 
                e.printStackTrace(); 
            }
            return i;
    }
    public static String[] getnum(int lang) throws IOException {
        String [] in=new String[lang];
        int i=0;
        try (FileReader reader = new FileReader("text.txt"); 
                BufferedReader br = new BufferedReader(reader)) 
            { 
            String line;  
            while ((line = br.readLine()) != null) {
                 in[i]= line;
                i++;
             }
            } 
            catch (IOException e)
            { 
                e.printStackTrace(); 
            }
            return in;
    }
    
        public   void writeFile() {
            int i=0;
            int fu=0;
            try {
                File writeName = new File("text.txt");
                writeName.createNewFile();
                try (FileWriter writer = new FileWriter(writeName);
                     BufferedWriter out = new BufferedWriter(writer)
                ) {
                    for(int j=0;j<150;j++) {
                        i=1+(int)(Math.random()*9);
                        //fu=1+(int)(Math.random()*2);
                        //if(fu==1)i=0-i;
                    out.write(i+"\r\n"); // \r\n换行
                    out.flush(); 
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        public static void add()  throws IOException {
            
            int i=0;
            try (FileReader reader = new FileReader("text.txt"); 
                    BufferedReader br = new BufferedReader(reader)) 
                { 
                String line;  
                while ((line = br.readLine()) != null) {
                    
                    i+=Integer.parseInt(line);
                 }
                } 
                catch (IOException e)
                { 
                    e.printStackTrace(); 
                }
            System.out.println("sum="+i);
        }


}