Counting occurences of integers in a java array

Question

I am trying to count occurrences of integers in an array. I would like to be able to modify the following loop that counts characters...

for (int i = 0; i < chars.length; i++)
     counts[chars[i] - 'a']++;

I tried modifying it like this but getting an ArrayIndexOutOfBoundsException error...

for (int i = 0; i < ints.length; i++)
     counts[ints[i] - '0']++;

Any ideas?

I have searched through many questions with similar titles but not in the fashion I need.

UPDATED

Here is my updated code. The user enters integers numbered 1 through 25. The program is supposed to count the occurrences of those integers using another array. I updated the code using...

counts[vals[i] - 1]++;

Which allows the program to compile. However, all the values of count are zeros.

UPDATED CODE...

import java.util.Scanner;


class CountIntOccurs
{
   private static final int MAX_NUM_OF_VALUES = 200;

   public static void main ( String [] args )
   {
      Scanner in = new Scanner( System.in );
      int[] vals = new int[MAX_NUM_OF_VALUES];
      int numOfVals = 0;

      // Read and store values
      System.out.println( "Enter integers <= 25, one per line, hit control-Z when done: " );
      while ( in.hasNextLine() )
      {
         vals[numOfVals] = Integer.parseInt( in.nextLine() );
         ++numOfVals;
      }

      // Close application if no values entered
      if ( numOfVals == 0 )
         System.exit( 0 );


      //  declare counts array   
      int[] counts = new int[25];


      System.out.println( counts.length );

      //??????? For each integer in the array, count it
      for (int i = 0; i < counts.length; i++){
         counts[vals[i] - 1]++; 
      }



      //display values enetered
      for ( int i = 0; i < numOfVals; ++i )
      {
            System.out.println( vals[i] );
      }


      //?????? display counted integers????
      for ( int i = 0; i < counts.length; ++i )
      {
            System.out.println( counts[i] );
      }


   }
}

Right now , what i need is to display the occurrences of the integers that are input. If I type in 1 1 2 2 2 the results should be 2 3 0 0 0 ... 0 .

Answer 1

The point of - 'a' is to subtract the ASCII value of 'a' (97) so that 'a' falls into index 0 and 'z' falls into index 25, the assumption being that chars only contains lowercase alphabetical characters.

Your code would work if ints was a char array containing numerical characters, that is, values between '0' and '9'. More likely, it's actually an int array, and by subtracting '0' (ASCII 48) you end up with a negative index.

To fix the problem, just remove the char subtraction:

counts[ints[i]]++;