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  1. #1
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    Jun 2011
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    Default Best Practice wrt Boxing / Unboxing

    Some people say that everything should be boxed.
    So instead of using primatives like int, you should always use their wrappers.
    But suppose I don't always want to copy references of my primatives into Hashtables and PriorityQueues etc.
    I might need to store some integers in a big 3 dimensional array like this:

    int[][][] arr = new int[64][64][64];

    Surely using the Integer object for this would be madness, wouldn't it create a lot of overhead?
    Unless that is if the compiller was able to automatically convert those Integer objects to ints, but does this really happen and if so how does it make that decision? Can I really be sure it will make the right choice?

  2. #2
    pbrockway2 is offline Moderator
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    Feb 2009
    New Zealand
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    Some people say that everything should be boxed.

    Which people? And for what reasons?

    One could make a case for a smalltalk-like "everything is an object" language (Sun bought LongView Technologies in 1997). But the Java we have is the Java we have and I can't see the gain in just not using some of the types it provides.

  3. #3
    JosAH's Avatar
    JosAH is offline Moderator
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    Sep 2008
    Voorschoten, the Netherlands
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    Note that the Integer class also caches some values for Integer objects; i.e. the value [0, 127] are kept in a cache and the method Integer.valueOf(int i) returns the same object over and over again for ints in the mentioned range. The choice what to autobox and to what wrapper type may not be intuitive; have a look at this cryptic example:

    Java Code:
    import java.util.ArrayList;
    import java.util.List;
    public class Autoboxing {
    	public static void main(String[] args) {
    		Object foo = new Long(0xcafebabedeadbeefL);
    		List<Object> bars = new ArrayList<Object>();
    		bars.add(true ? (Long)foo : (Long)foo);
    		bars.add(true ? (Long)foo : (Number)foo);
    		bars.add(true ? (Long)foo : (Double)foo);
    		bars.add(true ? (Long)foo : ((Long)foo).longValue());
    		System.out.print("==    :");
    		for (Object bar : bars)
    			System.out.print(" "+(foo == bar));
    		for (Object bar : bars)
    			 System.out.print(" "+foo.equals(bar));
    I find autoboxing a mixed blessing. In SmallTalk no primitives exist so this little problem doesn't exist in that language.

    kind regards,

    Build a wall around Donald Trump; I'll pay for it.

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