Java Multithreading make threads end in same order they started but run at same time

I have to make a program that searches through a bunch of lines from a file and tries to find a given substring. If it finds it, it prints out the line. Each line that I read is created as a thread and each thread searches a single line of the file. Thats not a problem so far. What I need the program to do is print the end results (the line of text) in the same order that the threads were created. I.E. thread 6 shouldnt be printing before thread 2. Its fine that the threads run at the same time, the printing order just needs to be maintained. I can not use the join method as I don't want the next one to wait for the other to finish entirely before starting, I do want them to be running at the same time. Any suggestions on doing this? Also, the file can have any number of lines so I cant hardcode the number of threads.

THE THREADS SHOULD DO THEIR OWN PRINTING. THE MAIN DOES NOT DO THE PRINTING.