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2009-10-24T16:11:41.763
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About <a href="http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.14.2" rel="noreferrer">the enhanced for statement</a>, the Java Language Specifications writes: <blockquote> The enhanced for statement has the form: <pre><code>EnhancedForStatement: for ( VariableModifiersopt Type Identifier: Expression) Statement </code></pre> The Expression must either have type <code>Iterable</code> or else it must be of an array type (§10.1), or a compile-time error occurs. The scope of a local variable declared in the FormalParameter part of an enhanced <code>for</code> statement (§14.14) is the contained Statement The meaning of the enhanced <code>for</code> statement is given by translation into a basic <code>for</code> statement. If the type of <code>Expression</code> is a subtype of <code>Iterable</code>, then let <code>I</code> be the type of the expression Expression.<code>iterator()</code>. The enhanced <code>for</code> statement is equivalent to a basic <code>for</code> statement of the form: <pre><code>for (I #i = Expression.iterator(); #i.hasNext(); ) { VariableModifiersopt Type Identifier = #i.next(); Statement } </code></pre> Where <code>#i</code> is a compiler-generated identifier that is distinct from any other identifiers (compiler-generated or otherwise) that are in scope (§6.3) at the point where the enhanced for statement occurs. Otherwise, the Expression necessarily has an array type, <code>T[]</code>. Let <code>L1 ... Lm</code> be the (possibly empty) sequence of labels immediately preceding the enhanced <code>for</code> statement. Then the meaning of the enhanced for statement is given by the following basic <code>for</code> statement: <pre><code>T[] a = Expression; L1: L2: ... Lm: for (int i = 0; i < a.length; i++) { VariableModifiersopt Type Identifier = a[i]; Statement } </code></pre> Where a and i are compiler-generated identifiers that are distinct from any other identifiers (compiler-generated or otherwise) that are in scope at the point where the enhanced for statement occurs. </blockquote> So in your case, <code>genArray()</code> doesn't return a subtype of <code>Iterable</code> but an array type, so your enhanced <code>for</code> statement is equivalent to the following basic <code>for</code> statement: <pre><code>String[] a = genArray(); ... for (int i = 0; i < a.length; i++) { String s = a[i]; // ... } </code></pre> And <code>genArray()</code> will thus be called only once (but the currently accepted answer is partially wrong).
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1. POIn a java enhanced for loop, is it safe to assume the expression to be looped over will be evaluated only once?
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1. POIn a java enhanced for loop, is it safe to assume the expression to be looped over will be evaluated only once?
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