Integer的缓存机制

        static final int low = -128;
        static final int high;
        static final Integer cache[];

Integer会有个常量数组，缓存 -128 到 127的值。 与此类似的还有Long

一、Integer类的缓存机制 二、其它具有缓存机制的类 面试题回到顶部我们查看Integer的源码,就会发现里面有个静态内部类。

* 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) {
        if (i >= IntegerCache.low && i <= IntegerCache.high)
            return IntegerCache.cache[i + (-IntegerCache.low)];
        return new Integer(i);
    }