Integer.valueOf(int i)源码中 assert

/**     * 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)            return IntegerCache.cache[i + (-IntegerCache.low)];        return new Integer(i);    }

assert的作用是计算表达式expression,

jdk1.7中存在，1.8中源码中已删除该代码。（频繁的调用会极大的影响程序的性能，增加额外的开销）

注意：有些地方，assert不能代替过滤条件

Other:

Integer.valueOf(int i)的范围

public static void main(String[] args) {    Integer a = 1;    Integer b = 1;    Integer c = 128;    Integer d = 128;    System.out.println(a==b);    System.out.println(c==d);}

代码执行结果：

truefalse