Can you explain the working principle of the `fork()` method in the `ForkJoinPool` class in Java?

The fork() method in the ForkJoinPool class is used to asynchronously start a task that implements the ForkJoinTask interface.

When you call fork() on a task, it is placed in the current thread's task queue (worker thread) and becomes available for execution by other pool threads. This allows parallel execution: one task can "branch out" into several subtasks that are executed concurrently.

Example of usage:

ForkJoinTask<Void> task = new RecursiveAction() {
    @Override
    protected void compute() {
        if (base_condition) {
            // perform work
        } else {
            RecursiveAction subtask1 = new Subtask(...);
            RecursiveAction subtask2 = new Subtask(...);
            subtask1.fork(); // asynchronously start the subtask
            subtask2.compute(); // execute the subtask synchronously
            subtask1.join(); // wait for the subtask to finish
        }
    }
};
task.invoke();

Thus, fork() puts the task in the execution queue, allowing other pool threads to take and execute it, which ensures efficient resource utilization and parallelism.