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    <p>You may refer following section / examples in <a href="http://docs.oracle.com/javase/specs/jls/se7/html/index.html" rel="noreferrer">Java language specification</a> that explains about the topic. </p> <ol> <li>Example 8.3.1.1-3. <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#d5e10238" rel="noreferrer">Hiding of Instance Variables</a></li> <li>Section 8.4.8. <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.4.8" rel="noreferrer">Inheritance, Overriding, and Hiding</a> and related examples</li> </ol> <p>Rest of my post is an additional information for those who are interested in scratching the surface of jvm internals on this subject. We can start by examining the byte codes generated for class A using javap. Following disassembles the byte codes into a human readable text based instructions (mnemonics).</p> <pre><code>javap -c A.class </code></pre> <p>Without getting lost in many details of the entire dis-assembly, we can focus on the lines corresponding to b.print and b.a</p> <pre><code>9: invokevirtual #4 // Method B.print:()V ... ... 16: getfield #6 // Field B.a:I </code></pre> <p>We can immediately infer that the op codes used for accessing the method and a variable are different. If you are from a C++ school, you could sense that all method calls are virtual by default in java.</p> <p>Now let us write another class A1 identical to A, but just has a casting for accessing variable 'a' in C. </p> <blockquote> <p>public class A1 {<br> &nbsp;&nbsp;public static void main(String[] args) {<br> &nbsp;&nbsp;&nbsp;&nbsp;B b=new C();<br> &nbsp;&nbsp;&nbsp;&nbsp;b.print(); //casting is irrelevant here because methods are anyway bound at runtime &nbsp;&nbsp;&nbsp;&nbsp;System.out.println(((C)b).a);// the casting allows us to access of value of a in C<br> &nbsp;&nbsp;}<br> } <br/></p> </blockquote> <p>Compile the file and disassemble the class. </p> <blockquote> <p>javap -c A1.class </p> </blockquote> <p>You would notice that dis-assembly now points to C.a instead of B.a </p> <blockquote> <p>19: getfield #6 // Field C.a:I</p> </blockquote> <p>if you want to dig deep into this, here goes additional information:<br> - invokevirtual corresponds to opcode 0xb6<br> - getfield corresponds to opcode 0xb4</p> <p>You can find a JVM specification that explains comprehensively about these opcodes at - <a href="http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html" rel="noreferrer">http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html</a><br> Check out in amazon.com for "Java Virtual Machine" books that could make life little more easier for decoding the specification.</p>
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    1. POwhy instance variable of super class is not overridden in sub class method
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    1. COThis is all completely unnecessary, and a very poor way to approach the problem. You only have to refer to the [Java Language Specification](http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#d5e10217) where these semantics are defined.
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    2. COYou are right from the aspect that the JVM internal may not be needed for a simple answer. But I think it is useful in some cases to look under the hood especially when we have a convenient tool such as javap. I have slightly altered the post. Let me know if you have any additional feedback.
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    3. COSince you asked for more feedback ... this is about as "useful" as a driving instructor telling a learner driver to "look under the hood" to find out how to start a car ... IMO.
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      1. USStephen C
 

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