Java. Why not the correct Leaf index?

Question

Java

When displaying the name of the current thread - everything happens correctly. And when I print the index of the same stream, I get -1. What am I doing wrong?

int countOfShips = scanner.nextInt();
        List<MyOwnThread> list = new ArrayList<>();

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                int randomIndex = (int) (Math.random() * ((countOfShips-1) - 0)) + 0;
                while (randomIndex == list.indexOf(Thread.currentThread())){
                    randomIndex = (int) (Math.random() * ((countOfShips-1) - 0)) + 0;
                }
                System.out.println(Thread.currentThread().getName());
                System.out.println(list.indexOf(Thread.currentThread()));
            }
        };

        for (int i = 0; i < countOfShips; i++) {
            list.add(i, new MyOwnThread());
            list.get(i).setHp(random.nextInt(51) + 50);
            list.get(i).setDamage(random.nextInt(11) + 20);
            list.get(i).setCoolDown(0.2f + random.nextDouble() * 1.5f);
            Thread thread = new Thread(runnable);
            list.get(i).setThread(thread);
            list.get(i).getThread().start();
            list.get(i).getThread().join();
        }

Answer 1

List.indexOf()returns -1 when it cannot find the argument passed to it in the list. In your example, the argument List.indexOf()is the class object Threadreturned by the call list.get(i).getThread()But you did not add such an object to the list.

Answer 2

because it appears to be a pointer to a stream object, not an element index in a list or a stream identifier.