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    <p>First of all, let's discuss what a "forward reference" is and why it is bad. A forward reference is a reference to a variable that has not yet been initialized, and it is not confined only to static initalizers. These are bad simply because, if allowed, they'd give us unexpected results. Take a look at this bit of code:</p> <pre><code>public class ForwardRef { int a = b; // &lt;--- Illegal forward reference int b = 10; } </code></pre> <p>What should j be when this class is initialized? When a class is initialized, initializations are executed in order the first to the last encountered. Therefore, you'd expect the line </p> <pre><code>a = b; </code></pre> <p>to execute prior to: </p> <pre><code>b = 10; </code></pre> <p>In order to avoid this kind of problems, Java designers completely disallowed such uses of forward references. </p> <p><strong>EDIT</strong></p> <p>this behaviour is specified by <a href="http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html" rel="nofollow noreferrer">section 8.3.2.3 of Java Language Specifications</a>:</p> <blockquote> <p>The declaration of a member needs to appear before it is used only if the member is an instance (respectively static) field of a class or interface C and all of the following conditions hold:</p> <ul> <li><p>The usage occurs in an instance (respectively static) variable initializer of C or in an instance (respectively static) initializer of C.</p></li> <li><p>The usage is not on the left hand side of an assignment.</p></li> <li><p>C is the innermost class or interface enclosing the usage.</p></li> </ul> <p>A compile-time error occurs if any of the three requirements above are not met.</p> </blockquote>
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    1. POWhy is the order of declarations important for static initializers?
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    1. COOK, I understand. But after the initial assignment myField *is* initialized. Why can't I still not call the add method?
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      1. USDaniel Rikowski
    2. COIf those three requirements were not there, I could create an implicit forward reference using local variables in the initializer, right? Is that the reason for these restrictions?
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      1. USDaniel Rikowski
    3. COths JLS says: "...These restrictions are designed to catch, at compile time, circular or otherwise malformed initializations...."
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      1. USCarlos Heuberger
 

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