Java Thread Test5 - Concurrency Problem

// Ttest5.java
// it contains a test java program, that defines a class jtest with
// a main function that prints howdy, and creates threads from the
// class Thread5.java
// It passes parameters to the threads, a name and an ID number.

// compile this file with the command "javac Ttest5.java"
// your path must include the bin directory of the jdk

// run the program with "java Ttest5"
// on some systems


class Ttest5 {
	public static void main(String argv[]) {
		System.out.println("Howdy from Ttest5");
  		new Thread5("Thread1", 0); //creates a thread
		new Thread5("Thread2", 1); //creates another thread
	}
}

//************* second file ******************************************

// Thread5.java
// It is a thread class to be run from Ttest5
// It receives parameters from the parent, a thread name and ID number
// The thread runs forever (until Ctrl-C at keyboard).
// Illustrates communication through shared-memory (static variables)
// Illustrates how to declare and instantiate an array.
// Illustrates concurrency problem: race conditions.
// Illustrates how to use random numbers.

// compile this file with the command "javac Thread5.java"
// your path must include the bin directory of the jdk

import java.lang.Math;
import java.util.Random;
public class Thread5 extends Thread {
	private int myid;	// private to this thread
	private int count;      // private count of iterations
	private int randwait;   // random amount of sleep time
	static int sharedarray[] = new int [4]; //static means one copy shared by
						//all the threads - shared memory
						//also shows how to create arrays
  	Random randGen;		// a pointer to a Random generator
	private int temp;	// holds sharedarray value temporarily

	Thread5(String name, int me) { //constructor - executed when thread is created with new
	   super(name); //super is part of the Thread class
	   myid=me;     
	   count = 0;   //initialize count
	   randGen = new Random(myid);	//instantiate randGen and seed the sequence
	   start(); // by default calls method "run"
	}

	public void run() {
	   while (true) {
	        count++;
		temp = sharedarray[0];		//all theads access same location
		randwait = (Math.abs(randGen.nextInt()) % 1000) +1;

		System.out.println("Howdy from " + Thread.currentThread().getName() + 
		",   id=" + myid + "  count is " + count + "  sharedarry[0]=" +
		sharedarray[0] + " random=" + randwait);

	        try {
                    Thread.sleep(randwait);     //milliseconds
                } catch (InterruptedException e) {
                    return;
		}
		sharedarray[0]=temp+1;		//introduce concurrency problem
	   }	
	}
}