Defining, Instantiating and starting thread

Threads can be created by extending Thread and overriding the public void run() method.

Thread objects can also be created by calling the Thread constructor that takes a Runnable argument. The Runnable object is said to be the target of the thread.

You can call start() on a Thread object only once. If start() is called more than once on a Thread object, it will throw a RuntimeException.

It is legal to create many Thread objects using the same Runnable object as the target.

When a Thread object is created, it does not become a thread of execution until its start() method is invoked. When a Thread object exists but hasn't been started, it is in the new state and is not considered alive.