What is the difference between `Thread` and `Runnable` in Java?
`Thread` is used to implement a task, while `Runnable` is used to create a new process for multithreading.
Actually, `Runnable` is not used to create a process; it defines a task to be executed by a thread. `Thread` creates and manages the actual thread.
Can you explain the role of the `start()` method in the `Thread` class?