java - How to debug a "ArrayIndexOutOfBoundsException" in my rail fence cipher program? -

here entire program encryption , decryption using rail fence cipher. arrayindexoutofboundsexception in last 4th line. please me understand , fix error.

import java.io.bufferedreader; import java.io.ioexception; import java.io.inputstreamreader;  /*  * change template, choose tools | templates  * , open template in editor.  */  /**  *  * @author pratheesh  */ public class test {  public void encrypt2(string line,int rail) {     int shift=0,p=0,itr;     for(int i=0;i<rail;i++)     {         p=i;         if(i==0||i==rail-1)         shift=((rail-2)*2)+2;         itr=1;         while(p<line.length())         {             system.out.print(line.charat(p));             if(i!=0&&i!=rail-1)             {                 shift=((rail*itr-itr)-p)*2;             }             p+=shift;             itr++;         }     } }  public void decrypt2(string line,int arr[]) {     int ptr[]=new int[arr.length+1];     int p1=0,p2=0,p3=0,c=1;     boolean chk=true;     system.out.print(line.charat(ptr[p3]+p1));     ptr[p3]++;     while(c<line.length())     {         if(chk)         {             p1+=arr[p2];             p2++;             p3++;         }         else         {             p1-=arr[p2];             p2--;             p3--;         }         system.out.print(line.charat(ptr[p3]+p1));         c++;         ptr[p3]++;         if(p2==arr.length)         {             p2--;             chk=false;         }         else if(p2==-1)         {             p2++;             chk=true;         }     }  }  public static void main(string args[]) throws ioexception, arrayindexoutofboundsexception{      test obj=new test();     string line;     int rail,arr[],temp;     line="password";     rail=integer.valueof(2);     temp=line.length()-rail;     int spaces;     if(temp%(rail-1)!=0)     {         spaces=(rail-1)-(temp%(rail-1));         if((temp/(rail-1))%2!=0)         {             spaces+=rail-1;         }     }     else     {         spaces=temp%(rail-1);         if((temp/(rail-1))%2==0)         {             spaces+=rail-1;         }     }     for(int g=0;g<spaces;g++)         line+=' ';     obj.encrypt2(line,rail);     //decryption     temp=line.length()-rail;     arr=new int[rail-1];     if((temp/(rail-1))%2==0)         arr[0]=1+(temp/(rail-1))/2;     else         arr[0]=1+((temp/(rail-1))+1)/2;     arr[1]=arr[0]*2-2;     for(int i=2;i<rail-1;i++)         arr[i]=arr[1]     obj.decrypt2(line,arr); } }     

when allocating new array, number in square brackets number of elements in array, not index of last element of array. if want array 2 elements, arr[0] , arr[1], need say

arr = new int[2];  // or expression value 2 

not

arr = new int[1];  // there 1 element, arr[0] 

i suspect error because you're trying assign arr[1] array has 1 element.