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    <p>You <em>can</em> use jMX beans to calculate a CPU load. Note that this measures CPU load of your java program, not the overall system load. (the question didn't specify which)</p> <p>Initialize:</p> <pre><code> ThreadMXBean newBean = ManagementFactory.getThreadMXBean(); try { if (this.newBean.isThreadCpuTimeSupported()) this.newBean.setThreadCpuTimeEnabled(true); else throw new AccessControlException(""); } catch (AccessControlException e) { System.out.println("CPU Usage monitoring is not available!"); System.exit(0); } </code></pre> <p>Then as your loop (assuming your application uses a loop, otherwise what's the point in measuring CPU usage?) use this:</p> <pre><code> long lastTime = System.nanoTime(); long lastThreadTime = newBean.getCurrentThreadCpuTime(); while (true) { // Do something that takes at least 10ms (on windows) try { int j = 0; for (int i = 0; i &lt; 20000000; i++) j = (j + i) * j / 2; Thread.sleep(100); } catch (InterruptedException e) { } // Calculate coarse CPU usage: long time = System.nanoTime(); long threadTime = newBean.getCurrentThreadCpuTime(); double load = (threadTime - lastThreadTime) / (double)(time - lastTime); System.out.println((float)load); // For next iteration. lastTime = time; lastThreadTime = threadTime; } </code></pre> <p>You need to use double precision because a long doesn't fit in a float (though it might work 99.9999999999999999% of the time)</p> <blockquote> <p>If the 'something' you're doing takes less than approximately 1.6ms (Windows), then the returned value will not even have increased at all and you'll perpetually measure 0% CPU erroneously.</p> </blockquote> <p>Because <code>getCurrentThreadCpuTime</code> is VERY inaccurate (with delays less than 100ms), smoothing it helps a lot:</p> <pre><code> long lastTime = System.nanoTime(); long lastThreadTime = newBean.getCurrentThreadCpuTime(); float smoothLoad = 0; while (true) { // Do something that takes at least 10ms (on windows) try { int j = 0; for (int i = 0; i &lt; 2000000; i++) j = (j + i) * j / 2; Thread.sleep(10); } catch (InterruptedException e) { } // Calculate coarse CPU usage: long time = System.nanoTime(); long threadTime = newBean.getCurrentThreadCpuTime(); double load = (threadTime - lastThreadTime) / (double)(time - lastTime); // Smooth it. smoothLoad += (load - smoothLoad) * 0.1; // damping factor, lower means less responsive, 1 means no smoothing. System.out.println(smoothLoad); // For next iteration. lastTime = time; lastThreadTime = threadTime; } </code></pre>
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