//Thread1.java
//A program can consist of multiple threads of execution,
//coordinating together to do multiple tasks at once.
//If multiprocessor, could be running simultaneously on separate CPUs.
//In uniprocessor, the threads can take turns at the CPU, thus lengthy
//task won't hold back others.
//Parallel/concurrent processing within the program.
//A thread is a lightweight process with its own call stack.
//The threads share the same memory space.
//Java has threading built-in to the language.


//Runnable interface has run() 
class X implements Runnable {
    public void run() {     //the required implementation
	//a thread has a getName()
	//Thread.currentThread() static method of Thread class refers to the execting thread
	System.out.println( "hi from a X thread. My name is " + 
			    Thread.currentThread().getName() );
    }
    //other methods and fields...called by run() (or whomever if not being
    //run by a thread).
}



public class Threads1 {
    public static void main( String[] args ) {
	//1. instantiate the Runnable class:
	X x1 = new X();     //an X object is the "work" to be done.
	//2. instantiate a Thread with your Runnable object as its "target":
	Thread t = new Thread( x1 );  //a thread is spun off to do the work in.
	//the work is done by the thread.
	//3. start the thread.   start() of Thread class.
	t.start();       //will call the Runnable's run()

	//main is a thread.  It and the t thread are running concurrently,
	//as if in parallel. 
	//main does NOT wait until the start() call returns.  main continues.
	//main thread and the t thread are sharing the processor.
	//the order in which threads execute is indeterminate.  

	//main thread's name is main 
	System.out.println( "hi from " + Thread.currentThread().getName() );



	//the x1 "job" can be given to many threads:
	Thread t2 = new Thread( x1 );
	Thread t3 = new Thread( x1 );
	Thread t4 = new Thread( x1 );
	//a thread has a setName() to replace the boring default name
	t2.setName( "gilligan" );
	t3.setName( "professor" );
	t4.setName( "his wife" );
	t2.start();
	t3.start();
	t4.start();
    }
}