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copied!<p>I just noticed you referenced <a href="http://javadude.com/articles/passbyvalue.htm" rel="noreferrer">my article</a>.</p> <p>The Java Spec says that everything in Java is pass-by-value. There is no such thing as "pass-by-reference" in Java.</p> <p>The key to understanding this is that something like</p> <pre><code>Dog myDog; </code></pre> <p>is <em>not</em> a Dog; it's actually a <em>pointer</em> to a Dog.</p> <p>What that means, is when you have</p> <pre><code>Dog myDog = new Dog("Rover"); foo(myDog); </code></pre> <p>you're essentially passing the <em>address</em> of the created <code>Dog</code> object to the <code>foo</code> method.</p> <p>(I say essentially because Java pointers aren't direct addresses, but it's easiest to think of them that way)</p> <p>Suppose the <code>Dog</code> object resides at memory address 42. This means we pass 42 to the method.</p> <p>if the Method were defined as</p> <pre><code>public void foo(Dog someDog) { someDog.setName("Max"); // AAA someDog = new Dog("Fifi"); // BBB someDog.setName("Rowlf"); // CCC } </code></pre> <p>let's look at what's happening.</p> <ul> <li>the parameter <code>someDog</code> is set to the value 42</li> <li>at line "AAA" <ul> <li><code>someDog</code> is followed to the <code>Dog</code> it points to (the <code>Dog</code> object at address 42)</li> <li>that <code>Dog</code> (the one at address 42) is asked to change his name to Max</li> </ul></li> <li>at line "BBB" <ul> <li>a new <code>Dog</code> is created. Let's say he's at address 74</li> <li>we assign the parameter <code>someDog</code> to 74 </li> </ul></li> <li>at line "CCC" <ul> <li>someDog is followed to the <code>Dog</code> it points to (the <code>Dog</code> object at address 74)</li> <li>that <code>Dog</code> (the one at address 74) is asked to change his name to Rowlf</li> </ul></li> <li>then, we return</li> </ul> <p>Now let's think about what happens outside the method:</p> <p><em>Did <code>myDog</code> change?</em></p> <p>There's the key.</p> <p>Keeping in mind that <code>myDog</code> is a <em>pointer</em>, and not an actual <code>Dog</code>, the answer is NO. <code>myDog</code> still has the value 42; it's still pointing to the original <code>Dog</code> (but note that because of line "AAA", its name is now "Max" - still the same Dog; <code>myDog</code>'s value has not changed.)</p> <p>It's perfectly valid to <em>follow</em> an address and change what's at the end of it; that does not change the variable, however.</p> <p>Java works exactly like C. You can assign a pointer, pass the pointer to a method, follow the pointer in the method and change the data that was pointed to. However, you cannot change where that pointer points.</p> <p>In C++, Ada, Pascal and other languages that support pass-by-reference, you can actually change the variable that was passed.</p> <p>If Java had pass-by-reference semantics, the <code>foo</code> method we defined above would have changed where <code>myDog</code> was pointing when it assigned <code>someDog</code> on line BBB.</p> <p>Think of reference parameters as being aliases for the variable passed in. When that alias is assigned, so is the variable that was passed in.</p>

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