【作业】返回一个整形数组中最大子数组地和--显示过程

package geren06;
import java.io.*;
import java.util.Scanner;
import java.util.ArrayList;
import java.util.InputMismatchException;
public class xianshi
{

    public static void main(String[] args)
    {
        long start = System.currentTimeMillis();
        Scanner input=new Scanner(System.in);
        int flag=0;
        int flag2=0;
        
            
            int LENGTH=20;//数量
            int FANWEI=10;//   n  :    -n   ~   +n
            int inum;
            int j=0;
            int m=0;
            int i=0,r=0,k=0;
            int n=0;
            String snum="";
            String fileName="number.txt";
            int [] num=new int[LENGTH];
             int array[]=new int[LENGTH];
             long maxsum=array[0];
             long maxstart=array[0];
            
            try
            {
                File f=new File(fileName);
                if(!f.exists())
                {
                    throw new Exception("文件"+fileName+"不存在");
                }
                
                //写入
                FileWriter fw=new FileWriter(f);
                PrintWriter pw=new PrintWriter(fw);
            //for(r=0;r<10;r++)
                //{
                    for( k=0;k<LENGTH;k++,m++)
                    {
                        inum=(int)(1+Math.random()*FANWEI*2)-FANWEI;
                        pw.print(inum+" ");
                        if(m==20)
                            {
                                pw.print("
");
                                m=0;
                            }
                    }
                    
                //}
            pw.flush();
                
                
                //读取
                do
                {
                    flag=0;
                    j=0;
                    m=0;
                    maxsum=array[0];
                    maxstart=array[0];
                    System.out.println("1 自动 2 单步（回车） 输入d倒带");
                    flag=input.nextInt();
                    input.nextLine();
                    if(flag2==1)
                    {
                        flag=1;
                    }
                    FileReader fr=new FileReader(f);
                    Scanner in=new Scanner(fr);
                    if(!in.hasNext())
                    {
                        throw new Exception("文件"+fileName+"内容为空");
                    }
                    
                    while(in.hasNext())
                    {
                        
                        if(j>=LENGTH)
                        
                        {
                            System.out.println("数字过多，多于"+LENGTH+"将不予读取");
                            break;
                        }
                         if(maxstart<0)
                            {
                             if(flag2==0)
                                 {
                                 System.out.print("		 "+m+"会使和变小 maxstart: 0");
                                 }
                                maxstart=0;
                            }
                         m=in.nextInt();
                         maxstart+=m;
                         if(flag==1&&flag2==0)
                         {
                                 Thread.sleep(1000);

                             System.out.println();
                         }
                         if(flag==2)
                         {
                             
                             if(input.nextLine().equals("d"))
                             {
                                 System.out.println("请输入序号：");
                                 n=input.nextInt();
                                 flag2=1;
                                 break;
                                 
                             }
                         }
                         if(flag2==0)
                         {
                             System.out.print("# j: "+j+"	");
                             System.out.print("m: "+m+"	");
                             System.out.print("maxstart: "+maxstart+"	");
                             System.out.print("maxsum: "+maxsum);
                         }
                        
                            
                            if(maxstart>=(Long.MAX_VALUE/2-1)||maxstart<=(Long.MIN_VALUE/2-1))
                            {
                                throw new Exception("数字过大溢出");
                            }
                            if(maxstart>maxsum)
                            {
                                if(flag2==0)System.out.print("		"+maxstart+" > "+maxsum+" --交换-- "+"maxsum:  "+maxsum);
                                maxsum=maxstart;
                            }
                                
                        j++;
                        if(j==n)
                        {
                            flag2=0;
                        }
                    }
                    if(flag2==1)
                    {
                        continue;
                    }
                    
                   
                    System.out.println("答案为：	"+maxsum);
                    System.out.println("是否继续?输入0结束");
                }while(flag!=0);
                

            }
            catch(InputMismatchException e2)
            {
                System.out.println("数字过大或输入格式不对");
            }
            catch(Exception e)
            {
                System.out.println("错误于：	"+i);
                System.out.println("错误！！！");
                System.out.println(e.getMessage());
                e.printStackTrace();
            }
            
            
                    long end = System.currentTimeMillis();
                    //System.out.println("程序运行时间："+(end-start)+"ms");
                    
                    
                    
        
                
                
        
    }
}

设立flag，合理使用if else。