Count Character in java

package homework;
import java.io.*;

public class Topic6 {
    public static void main(String[] args) throws IOException{
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        int num=0;
        int[] alpha = new int[26];
        char[] ch=null;
        System.out.print("How many character do you want to get(only lower case)? : ");
        num = Integer.parseInt(in.readLine());
        ch = new char[num];
        System.out.print("Characters : ");
        for(int i=0;i<ch.length;i++){
            ch[i]=(char)System.in.read();
        }
        for(int i=0;i<ch.length;i++)
            alpha[ch[i]-65]++;
       
        for(int i=1;i<=alpha.length;i++){
            System.out.print((char)(i+64)+"="+alpha[i-1]+"  ");
            if(i % 3== 0)
                System.out.println();
        }
    }
}