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    <p>First of all: I know it's hypocritical but I think the best place to get this idea solid in your head is to grab a Java textbook (or possibly an online tutorial). I don't think you'll be able to get a solid understanding of these concepts through our answers.</p> <p>Maybe try (I haven't read these, only skimmed):</p> <ul> <li><a href="http://www.yoda.arachsys.com/java/passing.html" rel="nofollow noreferrer">http://www.yoda.arachsys.com/java/passing.html</a></li> <li><a href="http://www.developertutorials.com/tutorials/java/pass-by-value-semantic-050524/page3.html" rel="nofollow noreferrer">http://www.developertutorials.com/tutorials/java/pass-by-value-semantic-050524/page3.html</a></li> <li><a href="http://javadude.com/articles/passbyvalue.htm" rel="nofollow noreferrer">http://javadude.com/articles/passbyvalue.htm</a></li> </ul> <hr> <p>I'm going to try and answer this a different way. The correct answer is out there already but this sort of thing is notoriously hard IMO to explain if you're not face-to-face with the person.</p> <p>This is your first piece of code:</p> <pre><code>public class Main { public static void foo(String a){ a="2"; } public static void main(String[] args) { String x="1"; foo(x); System.out.println("x="+x); } } </code></pre> <p>The problem is the line <code>a = "2"</code>. In simple terms it means: "make the variable 'a' point to a String instance with the value '2'". What this implies is: "forget whatever String 'a' is currently pointing to so it can point to this new value". So you are telling it to forget that it points to the String that you passed (as an argument to the method), so it can point to the new one.</p> <p>The String you passed as an argument still exists, and the variable 'x' still points to it. You didn't change the String which the variable 'x' points to, you only changed the String which the variable 'a' points to.</p> <p>As mentioned above this is because Java uses pass-by-value and not pass-by-reference.</p>
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    1. POReferences and variable passing. Explain the output of this simple java program?
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    1. POReferences and variable passing. Explain the output of this simple java program?
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    1. COThis is very helpful. So the = operator with string essentially does this? `public void set(String n){this.val=n.val}` (where n is the string to the right of the = operator)
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    2. COThe key here is to realise that the variables 'x', 'y', etc. just point to instances of String. They are not the String themselves. So you can point them to different Strings and they the String they pointed to is still uhnchanged (although it may now be lost forever). So saying `String x = "1"; String y = "2"; String z = x;` Will give you _x_ and _z_ pointing to the same String "1". You could then say `x = y;` and now x AND y will point to the _same_ String "2" and z will still be pointing to "1". This is the same for any Object (immutable or not) or primative.
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    3. COGot it! Thanks for sticking with me here. I get it now :)
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