Extending java Integer cache

问题

There's a general advice to use Integer.valueOf(int) instead of new Integer(int) because of caching.

In JDK 5+, you should really use valueOf because Integer now caches Integer objects between -128 and 127 and can hand you back the same exact Integer(0) object every time instead of wasting an object construction on a brand new identical Integer object.

How can extend the range?

回答1:

You can use the java.lang.Integer.IntegerCache.high property to increase the size of this cache.
ex :

java -Djava.lang.Integer.IntegerCache.high=4096 SomeClass.class

回答2:

My questions to you are:

1) Why is your code making new Integer objects hurting you? Do you have a profile result to share, to prove that making too many Integers is slowing your down? Object pooling, in general, is a BAD idea. You need a good case to justify it.

2) Why are you doing new Integer(int)? If you just keep it as a primitive int, not only will you avoid "creating a new object". you will not create any object at all. Auto boxing will handle converting it to an Integer if you need it at a later point in time.

*Disclaimer I Don't use EITHER.. I write performance sensitive code, but have never come to a point where I would manually turn a primitive int into an Integer. I just keep as an int whenever possible, and let the JVM autobox if it is needed.

回答3:

Extending the range of the cache may not get you what you are wanting, but if you have a real need to cache a greater range, you can use this code instead of Integer.valueOf(int). You just need to adjust the cache range values to the range you want.

private static class IntegerCache 
{
    private IntegerCache(){}

    static final Integer cache[] = new Integer[-(-128) + 127 + 1];

    static 
    {
        for(int i = 0; i < cache.length; i++)
        cache[i] = new Integer(i - 128); 
    }
}

public static Integer valueOf(int i) 
{
    final int offset = 128;
    if (i >= -128 && i <= 127) // must cache 
    {
        return IntegerCache.cache[i + offset];
    }
    return new Integer(i);
}

The code is from: http://www.owasp.org/index.php/Java_gotchas

回答4:

This is why the integer cache was added:

[...] to support the object identity semantics of autoboxing for values between -128 and 127 (inclusive), as required by the language specification.

If you profiled your app and you noticed that creating Integer objects is a hotspot, then by all means, copy the integer cache code and write your own with a different range. Otherwise your time would be better spent finding the real hotspots and improving those.

回答5:

Apparently, the -XX:+AggressiveOpts sets the max to 20000. See the answer on How large is the Integer cache?

来源：https://stackoverflow.com/questions/3934291/extending-java-integer-cache

标签

java

caching

integer

boxing