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PO
 

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    <p>Basically it's the pattern where you write a method to do things which are always required, e.g. resource allocation and clean-up, and make the caller pass in "what we want to do with the resource". For example:</p> <pre><code>public interface InputStreamAction { void useStream(InputStream stream) throws IOException; } // Somewhere else public void executeWithFile(String filename, InputStreamAction action) throws IOException { InputStream stream = new FileInputStream(filename); try { action.useStream(stream); } finally { stream.close(); } } // Calling it executeWithFile("filename.txt", new InputStreamAction() { public void useStream(InputStream stream) throws IOException { // Code to use the stream goes here } }); // Calling it with Java 8 Lambda Expression: executeWithFile("filename.txt", s -&gt; System.out.println(s.read())); // Or with Java 8 Method reference: executeWithFile("filename.txt", ClassName::methodName); </code></pre> <p>The calling code doesn't need to worry about the open/clean-up side - it will be taken care of by <code>executeWithFile</code>.</p> <p>This was frankly painful in Java because closures were so wordy, starting with Java 8 lambda expressions can be implemented like in many other languages (e.g. C# lambda expressions, or Groovy), and this special case is handled since Java 7 with <code>try-with-resources</code> and <code>AutoClosable</code> streams.</p> <p>Although "allocate and clean-up" is the typical example given, there are plenty of other possible examples - transaction handling, logging, executing some code with more privileges etc. It's basically a bit like the <a href="http://en.wikipedia.org/wiki/Template_method_pattern" rel="noreferrer">template method pattern</a> but without inheritance.</p>
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    1. POWhat is the "Execute Around" idiom?
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    1. USJon Skeet
    1. USJon Skeet
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    1. POWhat is the "Execute Around" idiom?
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    1. COHow is this different from a constructor and descructor which handle initialization and tear-down?
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      1. USNathan
    2. COIt's deterministic. Finalizers in Java aren't called deterministically. Also as I say in the last paragraph, it's not *only* used for resource allocation and cleanup. It may not need to create a new object at all. It's generally "initialization and tear-down" but that may not be resource allocation.
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      1. USJon Skeet
    3. COSo it's like in C where you have a function that you pass in a function pointer to do some work?
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      1. USPaul Tomblin
 

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