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    <p><a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.6.2" rel="nofollow noreferrer">Per the JLS</a>, <code>==</code> comparisons between a boxed and an unboxed value result in an <em>unboxing</em> conversion, not the other way around (or else you'd be using reference equality, not value equality). The compiler can't unbox a plain <code>Number</code>; <code>Number</code> itself isn't "convertible to <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2" rel="nofollow noreferrer">a numeric type</a>."</p> <p>The Java 7 compiler appears to be being clever. The assembly output for this version and for the version in which the comparison is moved into a <code>private</code> method completely ignore the declared type <code>Number</code>, and everything works properly. Make that method <code>public</code>, and the behavior is as specified: The conversion isn't one of the listed types for which unboxing will occur, and the compiler boxes <code>10</code> to an <code>Integer</code> and compares by reference, meaning that if you try using <code>Integer.valueOf(10)</code>, you'll get <code>true</code> for the range -128..127, and if you use anything else (another width, <code>new Integer(10)</code>), you'll get <code>false</code>.</p> <p>Output from your code (note that <code>Number</code> appears nowhere, and that you're getting comparison based on reference equality in line 18; try using <code>L</code> or casting to <code>short</code>):</p> <pre><code>public static void main(java.lang.String[]); Code: 0: bipush 10 2: invokestatic #2 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer; 5: astore_1 6: bipush 10 8: istore_2 9: getstatic #3 // Field java/lang/System.out:Ljava/io/PrintStream; 12: aload_1 13: bipush 10 15: invokestatic #2 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer; 18: if_acmpne 25 21: iconst_1 22: goto 26 25: iconst_0 26: invokevirtual #4 // Method java/io/PrintStream.println:(Z)V 29: return </code></pre> <p>Version that prevents optimization:</p> <pre><code>public class Test { public static void main(String[] args) { Number n = new Integer(10); compare(n); } public static void compare(Number n) { int i=10; System.out.println(n == 10); } } </code></pre> <p>Assembly; note that you're still getting a reference comparison in line 12:</p> <pre><code>public static void main(java.lang.String[]); Code: 0: new #2 // class java/lang/Integer 3: dup 4: bipush 10 6: invokespecial #3 // Method java/lang/Integer."&lt;init&gt;":(I)V 9: astore_1 10: aload_1 11: invokestatic #4 // Method compare:(Ljava/lang/Number;)V 14: return public static void compare(java.lang.Number); Code: 0: bipush 10 2: istore_1 3: getstatic #5 // Field java/lang/System.out:Ljava/io/PrintStream; 6: aload_0 7: bipush 10 9: invokestatic #6 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer; 12: if_acmpne 19 15: iconst_1 16: goto 20 19: iconst_0 20: invokevirtual #7 // Method java/io/PrintStream.println:(Z)V 23: return </code></pre>
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    1. POJava box then widen on == operator
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    1. CO[Here](http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.1.8) are the acceptable unboxing conversions.
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      1. USSotirios Delimanolis
    2. CO-1 This isn't what happens when you look at the byte code.
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    3. CO@chrylis can you point me exactly where it is stated that unboxing is prefered in place of boxing?
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