Java源码阅读-Integer

/**     * A constant holding the minimum value an {@code int} can     * have, -2<sup>31</sup>.     */    public static final int   MIN_VALUE = 0x80000000; // 最小值，-2的31次方    /**     * A constant holding the maximum value an {@code int} can     * have, 2<sup>31</sup>-1.     */    public static final int   MAX_VALUE = 0x7fffffff; // 最大值，2的31次方减1

valueOf方法

/**     * Returns an {@code Integer} instance representing the specified     * {@code int} value.  If a new {@code Integer} instance is not     * required, this method should generally be used in preference to     * the constructor {@link #Integer(int)}, as this method is likely     * to yield significantly better space and time performance by     * caching frequently requested values.     *     * This method will always cache values in the range -128 to 127,     * inclusive, and may cache other values outside of this range.     *     * @param  i an {@code int} value.     * @return an {@code Integer} instance representing {@code i}.     * @since  1.5     */    public static Integer valueOf(int i) {        assert IntegerCache.high >= 127;        if (i >= IntegerCache.low && i <= IntegerCache.high) // 如果在最大值和最小值之间，则使用缓存IntegerCache            return IntegerCache.cache[i + (-IntegerCache.low)];        return new Integer(i);    }

/**     * 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 -XX:AutoBoxCacheMax=<size> 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 { // 内部类，缓存        static final int low = -128;        static final int high;        static final Integer cache[];        static { // 静态代码块，Integer类被加载时则创建-128~127这些值放到数组中作为缓存            // 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) -1);            }            high = h;            cache = new Integer[(high - low) + 1];            int j = low;            for(int k = 0; k < cache.length; k++)                cache[k] = new Integer(j++);        }        private IntegerCache() {}    }