Java Automatic Unpacking traps

The use of Java automatic Unpacking is very extensive. But there are some "traps" in it. Nonsense not to say, to see a piece of code:

public static void Main (string[] args) {Integer a=1;integer b=2;integer c=3;integer d=3; System.out.println (c== (a+b)); System.out.println (C==d); System.out.println (C.equals (d)); Integer F=200;integer e=200; System.out.println (E==F); System.out.println (E.equals (f));

Printing results:

True

True

True

False

True

If all of the above operations are automatically disassembled, the printed result should be true. Here First explain the = = symbol does not occur automatically unpacking, so there are the above problems. But look closely, some people will say, that is not Ming C==d? In order to solve the mystery, we have to understand the boxing process. Let's take a look at the disassembly results for the above code:

From the above code snippet can be found that the original is called Integer.valueof This class method. Let's take a look at this class method:

  /**     * Returns a {@code integer} instance for the specified integer value.     * <p>     * If It isn't necessary to get a new {@code Integer} instance, it's * recommended to use the This     method Instead of the constructor, since it     * maintains a cache of instances which may result in better performance.     *     * @param i     * The            integer value to store in the instance.     * @return a {@code Integer} instance containing {@code i}.     * @since 1.5     *    /public static integer valueOf (int i) {        return  i >= | | i < -128? New integer (i): Small_values[i + +];    }

    /**     * A cache of instances used by {@link integer#valueof (int)} and auto-boxing     * *    private static final int eger[] small_values = new integer[256];

Seeing the above code, I believe it is clear why the above results have occurred. Because [-128,127] was cached.

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Java Automatic Unpacking traps