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POIs byte more efficient than boolean[8]
 

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    <p>If I need 8 boolean member variables in a class, does Java effectively place them all in one byte? Or will it use a byte for each? In other words, is the memory footprint different for:</p> <pre><code>boolean a; boolean b; boolean c; boolean d; boolean e; boolean f; boolean g; boolean h; </code></pre> <p>vs.</p> <pre><code>public static final int a = 0x01; public static final int b = 0x02; public static final int c = 0x04; public static final int d = 0x08; public static final int e = 0x10; public static final int f = 0x20; public static final int g = 0x40; public static final int h = 0x80; byte flags; </code></pre> <p>I'm asking because I will be instantiating a <strong>lot</strong> of these objects. So having it take 1 byte instead of 8 bytes of memory will be a noticeable savings.</p> <p><strong>Update:</strong> This is definitely similar to the linked questions that list that a boolean is stored in an int (thank you for those links and sorry I didn't find them before asking). This question is a little different in that it presents the specific alternative of using a byte and bit flags. I don't know if this is sufficient to make this question not a duplicate.</p> <p><strong>Update 2:</strong> I just ran this using <a href="https://code.google.com/p/core-java-performance-examples/source/browse/trunk/src/main/java/com/google/code/java/core/sizeof/SizeofUtil.java" rel="nofollow">SizeofUtil</a> and found the following. The 8 booleans requires 24 bytes/object or 3 bytes/boolean. The single byte approach requires 10 bytes/object. I would understand 8 where it's expanding a byte to a native int (I'm on a 64-bit system). But what's with the other 2 bytes?</p>
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    1. USDavid Thielen
    1. USDavid Thielen
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    1. COMy bet is that on 64 bit machine it will pack them 8 byes apart. But that's up to the JVM. Wasteful in terms of memory but not in terms of performance.
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      1. USBathsheba
    2. COyes it is more efficent
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      1. US0x90
    3. COFor self evident reasons the `boolean` must be the best data structure for holding booleans for usual requirements; otherwise something else would be used. I have a feeling that the usual requirements are probably access speed at the expense of memory. Do you want to sacrifice access speed?
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      1. USRichard Tingle
 

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