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    <p>1). You want your code to compile.</p> <p>Your compilation problems are because you're to declare your run methods within the main method. Separate you method declarations and then just use main to create &amp; run your threads.</p> <p>2). You want to have two threads operating concurrently. </p> <p>This means we need to either define two different thread classes or a single thread with logic to handle both incrementing and decrementing. Andrew Mao's answer gives you a start on how you might define two separate threads. My code above uses a single definition for a run method that uses a parameter to work out which way to go.</p> <p>3). You want to have two threads operating concurrently on the same data, because while they're incrementing/decrementing separately, they need to check for collisions.</p> <p>An easy way to do this is to create the objects you want to work on (num1 and num2) in your main method and then just pass references to these objects to your threads. Example in my code above.</p> <p>4). You want to test things</p> <p>All of java.lang.* is kind of assumed to be imported automatically. No harm in putting it there for clarity but auto-importer commands on your dev tool of choice will probably remove it as redundant.</p> <pre><code>public class ThreadExperiment implements Runnable { /* these fields are unique to each instance of ThreadExperiment */ private int increment = 0; /* these are used to point to the original num1 and num2 instances created in your main method */ private Integer myNumber; private Integer theOtherNumber; /** * Constructor. */ public ThreadExperiment(int increment, Integer num1Ref, Integer num2Ref) { this.increment = increment; this.myNumber = num1Ref; this.theOtherNumber = num2Ref; } @Override public void run() { do { myNumber += increment; try { Thread.sleep(400); } catch (InterruptedException e) { } System.out.println(Thread.currentThread().getName() + " -- " + myNumber); } while (!myNumber.equals(theOtherNumber)); } /** * Your static main method used to instantiate &amp; start threads */ public static void main(String[] args) { Integer num1 = 0; Integer num2 = 10; Thread t = new Thread(new ThreadExperiment(1, num1, num2), "Thread 1"); Thread t2 = new Thread(new ThreadExperiment(-1, num2, num1), "Thread 2"); t.start(); t2.start(); } } </code></pre>
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    1. COthank you kindly for the explanation - I read somewhere else on here that put the run methods in the main method, so clearly made a mistake, thank you for clearing that up. I have two questions though; what does the constructor do in your code? Also, I don`t understand the bit about parameter - where would said parameter be in the code?
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    2. COThe parameters are the variables that we pass into each Thread instance. Calling the constructor creates a new instance of the ThreadExperiment class, and in this case accepts a series of 3 parameters that configure that instance.
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