根据jls-5.1.7

If the value p being boxed is true, false, a byte, or a char in the range \u0000 to \u007f,

or an int or short number between -128 and 127 (inclusive), then let r1 and r2

be the results of any two boxing conversions of p. It is always the case that r1 == r2.

因此，Integer类将缓存-128到127之间的任何数字。

请记住，比较两个对象时，请始终使用IntegerCache方法。

缓存代码是IntegerCache类的成员，该类是Integer类的成员。

这是代码片段：

/**

* Cache to support the object identity semantics of autoboxing for values between

* -128 and 127 (inclusive) as required by JLS.

*

* The cache is initialized on first usage. The size of the cache

* may be controlled by the {@code -XX:AutoBoxCacheMax=} option.

* During VM initialization, java.lang.Integer.IntegerCache.high property

* may be set and saved in the private system properties in the

* sun.misc.VM class.

*/

private static class IntegerCache {

static final int low = -128;

static final int high;

static final Integer cache[];

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) {

try {

int i = parseInt(integerCacheHighPropValue);

i = Math.max(i, 127);

// Maximum array size is Integer.MAX_VALUE

h = Math.min(i, Integer.MAX_VALUE - (-low) -1);

} catch( NumberFormatException nfe) {

// If the property cannot be parsed into an int, ignore it.

}

}

high = h;

cache = new Integer[(high - low) + 1];

int j = low;

for(int k = 0; k < cache.length; k++)

cache[k] = new Integer(j++);

// range [-128, 127] must be interned (JLS7 5.1.7)

assert IntegerCache.high >= 127;

}

private IntegerCache() {}

}

参考文献

jls-5.1.7

整数类代码

整数Java文档