Java缓冲池

public class Main {
    public static void main(String[] args) {
        Integer a1 = new Integer(1);
        Integer a2 = new Integer(1);
        System.out.println(a1 == a2);
        System.out.println(a1.equals(a2));
    }
}

public class Main {
    public static void main(String[] args) {
        Integer a1 = new Integer(1);
        Integer a2 = new Integer(1);
        System.out.println(a1 == a2);
        System.out.println(a1.equals(a2));

        Integer a3 = new Integer(2);
        Integer a4 = a3;
        System.out.println(a3 == a4);
        System.out.println(a3.equals(a4));
    }
}

public class Main {
    public static void main(String[] args) {
        Integer a1 = new Integer(1);
        Integer a2 = new Integer(1);
        System.out.println(a1 == a2);
        System.out.println(a1.equals(a2));

        Integer a3 = new Integer(2);
        Integer a4 = a3;
        System.out.println(a3 == a4);
        System.out.println(a3.equals(a4));

        Integer a5 = 3;
        Integer a6 = 3;
        System.out.println(a5 == a6);
        System.out.println(a5.equals(a6));
    }
}

false
true
true
true
true
true

public class Main {
    public static void main(String[] args) {
        int min = 0;
        while (true) {
            Integer a1 = min;
            Integer a2 = min;
            if (a1 != a2) {
                ++min;
                System.out.print("[" + min + ", ");
                break;
            }
            --min;
        }

        int max = 0;
        while (true) {
            Integer a3 = max;
            Integer a4 = max;
            if (a3 != a4) {
                --max;
                System.out.println(max + "]");
                break;
            }
            ++max;
        }
    }
}

[-128, 127]

     /**
     * 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);
    }

    /**
     * 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() {}
    }