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POInconsistent behaviour of primitive integer types in Java
 

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    <p>Can someone explain to me like I'm five why I get different behaviour for two of four primitive types representing integers in Java? AFAIK all four are signed and they all use the most significant bit as a sign bit, so why do byte and short behave normally, and int and long act, well, strange? The fragment of oracle docs explaining this would be perfect.</p> <pre><code>byte a = (byte) (Math.pow(2, 7)-1); //127 - as expected short b = (short) (Math.pow(2, 15)-1); //32767 - as expected int c = (int) (Math.pow(2, 31)-1); //2147483647 - as expected long d = (long) (Math.pow(2, 63)-1); //9223372036854775807 - as expected a = (byte) (Math.pow(2, 7)); //-128 - as expected b = (short) (Math.pow(2, 15)); //-32768 - as expected c = (int) (Math.pow(2, 31)); //2147483647 - why not '-2147483648'? d = (long) (Math.pow(2, 63)); //9223372036854775807 - why not '-9223372036854775808'? a = (byte) (Math.pow(2, 8)); //0 - as expected b = (short) (Math.pow(2, 16)); //0 - as expected c = (int) (Math.pow(2, 32)); //2147483647 - why not '0'? d = (long) (Math.pow(2, 64)); //9223372036854775807 - why not '0'? </code></pre> <p>I'm using Oracle's Java SE 1.7 for Windows. OS is Windows 7 Professional SP1</p> <pre><code>java version "1.7.0_45" Java(TM) SE Runtime Environment (build 1.7.0_45-b18) Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode) </code></pre> <hr> <p><strong>EDIT, after reading all the answers and tuning my code.</strong><br/> So, to sum up, the only way I found to get expected values is the use of BigInteger. Shift operator works well for bytes, shorts and ints, but when it comes to longs, I cought it on one malfunction.</p> <pre><code>byte a = (byte) ((1l &lt;&lt; 7) - 1); //127 - as expected short b = (short) ((1l &lt;&lt; 15) - 1); //32767 - as expected int c = (int) (1l &lt;&lt; 31) - 1; //2147483647 - as expected long d = (1l &lt;&lt; 63) - 1; //9223372036854775807 - as expected a = (byte) (1l &lt;&lt; 7); //-128 - as expected b = (short) (1l &lt;&lt; 15); //-32768 - as expected c = (int) 1l &lt;&lt; 31; //-2147483648 - as expected d = 1l &lt;&lt; 63; //-9223372036854775808 - as expected a = (byte) (1l &lt;&lt; 8); //0 - as expected b = (short) (1l &lt;&lt; 16); //0 - as expected c = (int) (1l &lt;&lt; 32); //0 - as expected d = 1l &lt;&lt; 64; //1 instead of 0, probably because of the word length limitation </code></pre> <p>With BigInteger everything works flawlessly</p> <pre><code>byte a = (byte) (new BigInteger("2").pow(7).longValue() - 1); //127 - as expected short b = (short) (new BigInteger("2").pow(15).longValue() - 1); //32767 - as expected int c = (int) (new BigInteger("2").pow(31).longValue() - 1); //2147483647 - as expected long d = (new BigInteger("2").pow(63).longValue() - 1); //9223372036854775807 - as expected a = (byte) (new BigInteger("2").pow(7).longValue()); //-128 - as expected b = (short) (new BigInteger("2").pow(15).longValue()); //-32768 - as expected c = (int) new BigInteger("2").pow(31).longValue(); //-2147483648 - as expected d = new BigInteger("2").pow(63).longValue(); //-9223372036854775808 - as expected a = (byte) (new BigInteger("2").pow(8).longValue()); //0 - as expected b = (short) (new BigInteger("2").pow(16).longValue()); //0 - as expected c = (int) (new BigInteger("2").pow(32).longValue()); //0 - as expected d = new BigInteger("2").pow(64).longValue(); //0 - as expected </code></pre> <p><strong>Thanks everyone for big help!</strong></p>
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    1. COtry 2 << 7, 2 << 15, ... instead, it should be more precise
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    2. COGood tip. Thanks
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