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Yes now its working, Thank you !!

No I didn't found the String with the null value.
java version "16.0.1" 2021-04-20
Java(TM) SE Runtime Environment (build 16.0.1+9-24)

--- Update ---



When we are running sequentially it...

When I'm running it with one thread it is running smoothly, it is not giving any error. But when I'm running 4 threads, it is giving the above said error.

[b] This is the error I'm getting [\b]

[exception]

Exception in thread "Thread-1" java.lang.NullPointerException: Cannot invoke "String.length()" because "str" is null
at...

[QUOTE] How to add pictures from computer ? So I can add pictures for better understanding ? PS. I am new to Java Programming Forums [/QUOTES]

--- Update ---

The code is running when I'm running single thread but it throwing error when I'm trying to run multiple threads.

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ok thank you !

public class Main extends Thread
{

class credit extends Thread
{
public void run()
{


String filename="Credit_card.txt";