for (int i = 0; i < 150; i++) {

                 Integer a = i;

                 Integer b = i;

                 System.out.println(i + " " + (a == b));

             }部分结果

.....
124 true

125 true

126 true

127 true

128 false

129 false

130 false

131 false

for(int i=0;i<150;i++){

    Integer a=i;

    Integer b=i;

    System.out.println(a+" "+b+" "+System.identityHashCode(a)+" "+System.identityHashCode(b));

}

1 123 123 1531448569 1531448569

 124 124 1867083167 1867083167

 125 125 1915910607 1915910607

 126 126 284720968 284720968

 127 127 189568618 189568618

 128 128 793589513 1313922862

 129 129 495053715 1922154895

    /**

     * 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);

    }