for循环在比较Integer.MAX_VALUE和使用System.out.println时提前终止 [英] for loop terminating early when comparing to Integer.MAX_VALUE and using System.out.println
问题描述
当我运行这个类的时候,for循环似乎很快就终止了
class Test {
public static void main(String [] args){
int result = 0;
int end = Integer.MAX_VALUE;
int i; (i = 1; i< = end; i + = 2)
System.out.println(i);
}
System.out.println(End:+ i);
}
}
输出结果是:
1
3
5
...
31173
31175
结尾:31177
为什么结束?有趣的是,如果我在for循环中删除了 我正在使用的Java版本是 System.out.println(i)
,输出将是结束:-2147483647
。很明显, i
中的值包含> 。
pre $ Java $ SE运行时环境(build 1.6.0_16-b01)
Java HotSpot(TM)64位服务器虚拟机(构建14.2-b01,混合模式)
它是Java 6中的一个已知错误.JIT错误地优化了循环。我相信更新的Java版本没有这个bug。
http://vanillajava.blogspot.co.uk/2011/05/when-jit-gets-it-wrong.html
Java 6 update 16已经过了两年多了。我建议你更新到最新版本的Java 6更新25,如果你不能更新到Java 7.
顺便提一下,Java 6将是免费支持个月(2012年12月)
When I run this class the for loop seems to terminate early
class Test {
public static void main(String[] args) {
int result = 0;
int end = Integer.MAX_VALUE;
int i;
for (i = 1; i <= end; i += 2) {
System.out.println(i);
}
System.out.println("End:" + i);
}
}
Output is:
1
3
5
...
31173
31175
End:31177
Why does it end there? Interestingly if I removed the System.out.println(i)
in the for loop, the output would be End:-2147483647
. Obviously the value in i
has wrapped round
.
The Java version I'm using is
Java(TM) SE Runtime Environment (build 1.6.0_16-b01)
Java HotSpot(TM) 64-Bit Server VM (build 14.2-b01, mixed mode)
Its a known bug in Java 6. The JIT optimizes the loop incorrectly. I believe more recent versions of Java don't have this bug.
http://vanillajava.blogspot.co.uk/2011/05/when-jit-gets-it-wrong.html
Java 6 update 16 is just over two years old. I suggest you update to the latest version Java 6 update 25 if you can't update to Java 7.
BTW Java 6 will be End Of Free Support in a couple of months (Dec 2012)
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