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copied!<p>Java doesn't support true <a href="http://en.wikipedia.org/wiki/Closure_(computer_science)" rel="noreferrer">closures</a>, even though using an anonymous class like you are using here (<code>new TimerTask() { ... }</code>) looks like a kind of closure.</p> <p><strong>edit</strong> - <em>See the comments below - the following is not a correct explanation, as KeeperOfTheSoul points out.</em></p> <p>This is why it doesn't work:</p> <p>The variables <code>lastPrice</code> and price are local variables in the main() method. The object that you create with the anonymous class might last until after the <code>main()</code> method returns.</p> <p>When the <code>main()</code> method returns, local variables (such as <code>lastPrice</code> and <code>price</code>) will be cleaned up from the stack, so they won't exist anymore after <code>main()</code> returns.</p> <p>But the anonymous class object references these variables. Things would go horribly wrong if the anonymous class object tries to access the variables after they have been cleaned up.</p> <p>By making <code>lastPrice</code> and <code>price</code> <code>final</code>, they are not really variables anymore, but constants. The compiler can then just replace the use of <code>lastPrice</code> and <code>price</code> in the anonymous class with the values of the constants (at compile time, of course), and you won't have the problem with accessing non-existent variables anymore.</p> <p>Other programming languages that do support closures do it by treating those variables specially - by making sure they don't get destroyed when the method ends, so that the closure can still access the variables.</p> <p>@Ankur: You could do this:</p> <pre><code>public static void main(String args[]) { int period = 2000; int delay = 2000; Timer timer = new Timer(); timer.scheduleAtFixedRate(new TimerTask() { // Variables as member variables instead of local variables in main() private double lastPrice = 0; private Price priceObject = new Price(); private double price = 0; public void run() { price = priceObject.getNextPrice(lastPrice); System.out.println(); lastPrice = price; } }, delay, period); } </code></pre>

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