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POCan I initialize a static member once and share it across threads?
 

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  1. POCan I initialize a static member once and share it across threads?
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    <p>This is my first time attempting to write a program that makes use of multithreading, so I have several questions regarding the use of concurrency in my program.</p> <p>My program takes user input from a web UI, and then starts a process with that user input. I know I have to make use of concurrency because this process takes upwards of an hour, and I cannot possibly have the user wait for one process to complete before starting the next.</p> <p>The following simplified code handles the user input and then starts the process.</p> <pre><code>protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String myInput = request.getParameter("input"); Thread t = new Thread(new MyRunnable(myInput)); t.start(); response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("Process started!"); out.close(); } </code></pre> <p>The following code is a simplification of my actual process.</p> <pre><code>public class MyRunnable implements Runnable { private static HashMap&lt;String,String&gt; mapOfConstants = null; private String member; public MyRunnable(String member) { this.member = member; } @Override public void run() { if (mapOfConstants == null) init(); // and so on... } private void init() { mapOfConstants = new HashMap&lt;String,String&gt;(); mapOfConstants.put("LOCATION", "http://localhost/folder"); // and so on... } } </code></pre> <p>In my code above, I intend to define a series of placeholders as a constant, which will be stored in the HashMap <code>mapOfConstants</code>.</p> <p>EDIT: Eventually I might want to make it such that initialization of this map take values from elsewhere, say a text file.</p> <p>Does my code achieve the purpose of sharing this placeholder map across all instances of <code>MyRunnable</code>, doing this initialization process only once?</p>
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    1. COFor starters you could make your map `final` and initialize it at declaration time.
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    2. COPlease don't ask for multiple answers in one Stack Overflow question. Edit your question to include just one question and post a follow-up question if necessary.
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    3. COEdited my question and clarified my intentions
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