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copied!<p>It's worth mentioning that the following expression:</p> <pre><code>new Long(10).equals(new Integer(10)) </code></pre> <p>is always <code>false</code>, which tends to trip everyone up at some point or another. So not only can you not compare arbitrary <code>Number</code>s but you can't even determine if they're equal or not.</p> <p>Also, with the real primitive types (<code>float</code>, <code>double</code>), determining if two values are equal is tricky and has to be done within an acceptable margin of error. Try code like:</p> <pre><code>double d1 = 1.0d; double d2 = 0.0d; for (int i=0; i<10; i++) { d2 += 0.1d; } System.out.println(d2 - d1); </code></pre> <p>and you'll be left with some small difference.</p> <p>So back to the issue of making <code>Number</code> <code>Comparable</code>. How would you implement it? Using something like <code>doubleValue()</code> wouldn't do it reliably. Remember the <code>Number</code> subtypes are:</p> <ul> <li><code>Byte</code>;</li> <li><code>Short</code>;</li> <li><code>Integer</code>;</li> <li><code>Long</code>;</li> <li><code>AtomicInteger</code>;</li> <li><code>AtomicLong</code>;</li> <li><code>Float</code>;</li> <li><code>Double</code>;</li> <li><code>BigInteger</code>; and</li> <li><code>BigDecimal</code>.</li> </ul> <p>Could you code a reliable <code>compareTo()</code> method that doesn't devolve into a series of if instanceof statements? <code>Number</code> instances only have six methods available to them:</p> <ul> <li><code>byteValue()</code>;</li> <li><code>shortValue()</code>;</li> <li><code>intValue()</code>;</li> <li><code>longValue()</code>;</li> <li><code>floatValue()</code>; and</li> <li><code>doubleValue()</code>.</li> </ul> <p>So I guess Sun made the (reasonable) decision that <code>Number</code>s were only <code>Comparable</code> to instances of themselves.</p>

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