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    <p>Java is always <strong>pass-by-value</strong>. Unfortunately, they decided to call the location of an object a "reference". When we pass the value of an object, we are passing the <em>reference</em> to it. This is confusing to beginners.</p> <p>It goes like this:</p> <pre><code>public static void main(String[] args) { Dog aDog = new Dog("Max"); // we pass the object to foo foo(aDog); // aDog variable is still pointing to the "Max" dog when foo(...) returns aDog.getName().equals("Max"); // true aDog.getName().equals("Fifi"); // false } public static void foo(Dog d) { d.getName().equals("Max"); // true // change d inside of foo() to point to a new Dog instance "Fifi" d = new Dog("Fifi"); d.getName().equals("Fifi"); // true } </code></pre> <p>In the example above <code>aDog.getName()</code> will still return <code>"Max"</code>. The value <code>aDog</code> within <code>main</code> is not changed in the function <code>foo</code> with the <code>Dog</code> <code>"Fifi"</code> as the object reference is passed by value. If it were passed by reference, then the <code>aDog.getName()</code> in <code>main</code> would return <code>"Fifi"</code> after the call to <code>foo</code>.</p> <p>Likewise:</p> <pre><code>public static void main(String[] args) { Dog aDog = new Dog("Max"); foo(aDog); // when foo(...) returns, the name of the dog has been changed to "Fifi" aDog.getName().equals("Fifi"); // true } public static void foo(Dog d) { d.getName().equals("Max"); // true // this changes the name of d to be "Fifi" d.setName("Fifi"); } </code></pre> <p>In the above example, <code>Fifi</code> is the dog's name after call to <code>foo(aDog)</code> because the object's name was set inside of <code>foo(...)</code>. Any operations that <code>foo</code> performs on <code>d</code> are such that, for all practical purposes, they are performed on <code>aDog</code> itself (except when <code>d</code> is changed to point to a different <code>Dog</code> instance like <code>d = new Dog("Boxer")</code>).</p>
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    1. POIs Java "pass-by-reference" or "pass-by-value"?
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    1. COIsn't it slightly confusing the issue with internal details? There's no conceptual difference between 'passing a reference' and 'passing the value of a reference', assuming that you mean 'the value of the internal pointer to the object'.
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    2. COBut there is a subtle difference. Look at the first example. If it was purely pass by reference, aDog.name would be "Fifi". It isn't - the reference you are getting is a value reference that if overwritten will be restored when exiting the function.
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    3. CObeware however that integral types are passed by value and not by reference. Also immutable types are passed by reference but "kinda" works as passing them by value: the most common example would be String. This allow for internal space optimization of immutable objects.
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      1. USLorenzo Boccaccia
 

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