设置IntegerCache的上界

[dreamhunter_lan]

用-D可以设置java.lang.Integer.IntegerCache.high，将上限设置大于127，但是当我把它置为小于127（比如20），
然后
Integer a = 10;
Integer b = 10;
System.out.println(a == b);
打出false
不知为何

[dreamhunter_lan]

囧了，之前估计是忘记重新编译了，NND~~~谢了

[huntor]

小于127没效果。

static {
            // high value may be configured by property
            int h = 127;
            String integerCacheHighPropValue =
                sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
            if (integerCacheHighPropValue != null) {
                int i = parseInt(integerCacheHighPropValue);
                i = Math.max(i, 127);
                // Maximum array size is Integer.MAX_VALUE
                h = Math.min(i, Integer.MAX_VALUE - (-low));
            }
            high = h;

            cache = new Integer[(high - low) + 1];
            int j = low;
            for(int k = 0; k < cache.length; k++)
                cache[k] = new Integer(j++);
        }

[dreamhunter_lan]

[Quote=引用 1 楼 huntor 的回复:]

小于127没效果。
Java code
static {
// high value may be configured by property
int h = 127;
String integerCacheHighPropValue =
sun.misc.VM.getSavedProp……
[/Quote]
就算没效果，我那个例子不应该还是返回true吗？因为上界一定会大于等于127的，所以一定在Cache中

[huntor]

-Djava.lang.Integer.IntegerCache.high=20

java version "1.7.0"
Java(TM) SE Runtime Environment (build 1.7.0-b147)
Java HotSpot(TM) Client VM (build 21.0-b17, mixed mode, sharing)

java version "1.6.0_27"
Java(TM) SE Runtime Environment (build 1.6.0_27-b07)
Java HotSpot(TM) Client VM (build 20.2-b06, mixed mode, sharing)

java version "1.6.0_26"
Java(TM) SE Runtime Environment (build 1.6.0_26-b03)
Oracle JRockit(R) (build R28.1.4-7-144370-1.6.0_26-20110617-2130-linux-ia32, compiled mode)

java version "1.6.0"
Java(TM) SE Runtime Environment (build pxi3260sr9fp2-20110625_01(SR9 FP2))
IBM J9 VM (build 2.4, JRE 1.6.0 IBM J9 2.4 Linux x86-32 jvmxi3260sr9-20110624_85526 (JIT enabled, AOT enabled)
J9VM - 20110624_085526
JIT - r9_20101028_17488ifx17
GC - 20101027_AA)
JCL - 20110530_01

都是返回 true