Running correctly but getting Runtime error 'NZEC' while submitting

I was solving this problem: Safe Robots
In custom input section after providing inputs and running, it ran fine and no issues were reported, but when I SUBMIT IT GIVES ‘NZEC Runtime error’.

Code is given below:

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;

//coded by leucocephalus, this is JAVA Code, so don't mind the length of it :)
class Codechef
{
    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }


        public StringBuffer readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }

            StringBuffer stringBuffer = new StringBuffer(new String(buf,0,cnt));
            return stringBuffer;
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }



    public static void main(String args[]) throws IOException {

        Reader rd = new Reader() ;
        int T=rd.nextInt() ;

        while (T-->0){
            String plc = rd.readLine().toString() ;
            int L = plc.indexOf('B') - plc.indexOf('A');
            int a = rd.nextInt(), b=rd.nextInt() ;
            if(L%(a+b)==0) System.out.println("unsafe"); else System.out.println("safe");
        }

    }
}

Kindly tell me why this is happening, and whats the fix for this bug…
Thanks in advance, waiting to be rescued soon.

Exception in thread “main” java.lang.ArrayIndexOutOfBoundsException: 65536
at Codechef$Reader.read(Main.java:121)
at Codechef$Reader.nextInt(Main.java:50)
at Codechef.main(Main.java:137)

lines 50 121 137 being-

while (c <= ’ ')
c = read();
return buffer[bufferPointer++];
int T=rd.nextInt() ;

i would say the best way is to take input using simple BufferedReader(atleast for easy level problems). A lot less to type and a lot less to recheck.