I am using threading in my code and initializing it inside a while loop.
it executed successfully for 31 iterations, however after that for 5 remaining iterations it throws null pointer exception.

threads[i] = new Thread(new MyTask(a, b, c, keyValuePairs, d)); threads[i].start();

and then using thread join

try {
    for (Thread thread : threads) {
    thread.join(); // Wait for each thread to finish
    }
} catch (Exception e) {
    e.printStackTrace();
    System.out.println("Thread Execution failed");
}

full code snip

for (int j = 0; j < LoopCount; j++) {
    if (cnt >= 15) {
        op = 15;
    } else {
        op = cnt;
    }
    cnt = cnt - 15;
    Thread[] threads = new Thread[op];
    ResultSet resultSet = stmt.executeQuery(sqlQuery);
    int i = 0;
    long a = 0;
    String b;
    String c;
    String d;
    while (resultSet.next() && i < op) {

        a = resultSet.getLong("a");
        b = resultSet.getString("b");
        c = resultSet.getString("c");
        d = resultSet.getString("d");

        sqlQuery3 = "UPDATE IBL_PAYMENT_STG_TBL SET RESPONSEFLAG = 'IP'  WHERE xyz = " + a;
        UpdateStmt.executeQuery(sqlQuery3);
        threads[i] = new Thread(new MyTask(a, b, c, keyValuePairs, d));
        threads[i].start();
        i++;
    }

    resultSet.close();


    try {
        for (Thread thread : threads) {
            thread.join(); // Wait for each thread to finish
        }


    } catch (Exception e) {
        e.printStackTrace();``your text``
        System.out.println("Thread Execution failed");
    }
}