practice code?

class Prime {
    public static void main(String args[]) throws IOException {
        int a, b, i, j, flag;
        // DataInputStream would not have been my first choice here
        DataInputStream ds = new DataInputStream(System.in); // missing semicolon
        System.out.println("Enter lower bound of the interval:");
        a = Integer.parseInt(ds.readLine());
        System.out.println("Enter upper bound of the interval:");
        b = Integer.parseInt(ds.readLine());
        System.out.println("\nPrime number between " + a + " and " + b + " are:"); // \n instead of /n

        for (i = a; i <= b; i++) {
            if (i == 1 || i == 0) // = is an assignment, == used for comparison
                continue;

            flag = 0;
            for (j = 2; j <= i / 2; j++) {
                if (i % j == 0) { // you probably didn't want to divide the operands
                    flag = 1; // missing semicolon
                    break;
                }
            }

            if (flag == 0) // missing parenthesis
                System.out.println(i);
        }
    }
}