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POJava: Inaccuracy using double
 

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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/322749/retain-precision-with-doubles-in-java">Retain precision with Doubles in java</a><br> <a href="https://stackoverflow.com/questions/327544/strange-floating-point-behaviour-in-a-java-program">Strange floating-point behaviour in a Java program</a> </p> </blockquote> <p>I'm making a histogram class, and I'm encountering a weird issue.</p> <p>Here are the basics of the class, there are more methods but they aren't relevant to the issue.</p> <pre><code>private int[] counters; private int numCounters; private double min, max, width; public Histogram(double botRange, double topRange, int numCounters) { counters = new int[numCounters]; this.numCounters = numCounters; min = botRange; max = topRange; width = (max - min) / (double) numCounters; } public void plotFrequency() { for (int i = 0; i &lt; counters.length; i++) { writeLimit(i * width, (i + 1) * width); System.out.println(counters[i]); } } private void writeLimit(double start, double end) { System.out.print(start + " &lt;= x &lt; " + end + "\t\t"); } </code></pre> <p>the problem happens when I plot the frequencies. I've created 2 instances. new Histogram(0, 1, 10); new Histogram(0, 10, 10);</p> <p>This is what they output.</p> <pre><code>Frequecy 0.0 &lt;= x &lt; 0.1 989 0.1 &lt;= x &lt; 0.2 1008 0.2 &lt;= x &lt; 0.30000000000000004 1007 0.30000000000000004 &lt;= x &lt; 0.4 1044 0.4 &lt;= x &lt; 0.5 981 0.5 &lt;= x &lt; 0.6000000000000001 997 0.6000000000000001 &lt;= x &lt; 0.7000000000000001 1005 0.7000000000000001 &lt;= x &lt; 0.8 988 0.8 &lt;= x &lt; 0.9 1003 0.9 &lt;= x &lt; 1.0 978 Frequecy 0.0 &lt;= x &lt; 1.0 990 1.0 &lt;= x &lt; 2.0 967 2.0 &lt;= x &lt; 3.0 1076 3.0 &lt;= x &lt; 4.0 1048 4.0 &lt;= x &lt; 5.0 971 5.0 &lt;= x &lt; 6.0 973 6.0 &lt;= x &lt; 7.0 1002 7.0 &lt;= x &lt; 8.0 988 8.0 &lt;= x &lt; 9.0 1003 9.0 &lt;= x &lt; 10.0 982 </code></pre> <p>So my question is, why am I getting the really long decimal limits in the first example, but not the second one?</p>
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    1. COThis has all to do with the inaccuracies inherent when trying to do floating point arithmetic using digital hardware. This is not limited to Java but to any and all programming language and has been asked and answered over a thousand times on this and other sites. See for example [The Perils of Floating Point](http://www.lahey.com/float.htm)
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    2. COhttp://stackoverflow.com/questions/1661273/java-floating-point-arithmetic and http://stackoverflow.com/questions/327544/strange-floating-point-behaviour-in-a-java-program and ...
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    3. COFYI, this is a result of the standard set by IEEE (754). There are ways around these precision problems in Java. See BigDecimal: http://download.oracle.com/javase/1,5.0/docs/api/index.html?java/math/BigDecimal.html
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