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POProblems with Java HashMaps and putAll() method
 

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  1. POProblems with Java HashMaps and putAll() method
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    <p>Hey everybody, I am writing a program that compares the running times of various Dijkstra implementations. I parse the relevant info from a text file and enter it into a hashtable. In my current implementation I have a 'master' hashtable that holds the Node info and that info is copied into a temporary hashtable which is then passed onto different Dijkstra classes. </p> <pre><code>public class Router { public static Map &lt;Integer, Node&gt; nodes = new HashMap&lt;Integer, Node&gt;(); public static Map &lt;Integer, Node&gt; temp = new HashMap&lt;Integer, Node&gt;(); public static int target = 2; public static int start = 0; public static void main(String[] args) throws IOException { Parser p3 = new Parser(args[0], nodes, p); temp.putAll(nodes); // Test 1 DijkstraFib fb = new DijkstraFib(temp, start, target, p); temp.clear(); temp.putAll(nodes); //Test 2 DijkstraBinary d = new DijkstraBinary(temp, start, target, p); temp.clear(); temp.putAll(nodes); // Test 3 Dijkstra b = new Dijkstra(temp, start, target, p); } </code></pre> <p>}</p> <p>So rather then having to invoke a parser three times for each Dijkstra class, I simply want to copy all the values from <code>nodes</code> table to <code>temp</code>, since <code>temp</code> gets modified during the method execution. The first two tests run fine, but the third test fails. If I swap Test 2 and Test 3 around then Test 2 fails; basically, whichever test is run last, fails. Here's my Dijkstra method:</p> <pre><code>void route(Map &lt;Integer, Node&gt; nodes, int source) { Node start = nodes.get(source); start.distance = 0; unsettledNodes.add(start); while(!unsettledNodes.isEmpty()) { Node n = extractMin(); visited.put(n.name, n); relax_neighbours(n, nodes); } } void relax_neighbours(Node n, Map &lt;Integer, Node&gt; nodes) { for (int i = 0; i &lt; n.outgoing.size(); i++) { Edge edge = n.outgoing.get(i); Node v = nodes.get(edge.node); if (isSettled(v)) { continue; } double shortDist = n.distance + edge.length; if (shortDist &lt; v.distance) { unsettledNodes.remove(v); v.distance = shortDist; v.previous = n; unsettledNodes.add(v); } } } </code></pre> <p>and here's my method that prints the path starting from the target node:</p> <pre><code> void print_path(Map &lt;Integer, Node&gt; visited, int i) { ArrayList&lt;Node&gt; path = new ArrayList&lt;Node&gt;(); for (Node target = visited.get(i); target != null; target = target.previous) { path.add(target); } System.out.println("Simple Dijkstra took " + this.time_taken + " ms"); System.out.print("Min dist from " + this.source + " to " + this.target + " = " + path.get(0).distance + " : "); Collections.reverse(path); System.out.print(path.get(0).name); p.append(Integer.toString(path.get(0).name)); for (int k = 1; k &lt; path.size(); k++) { System.out.print(" -&gt; " + path.get(k).name); } System.out.println(); } </code></pre> <p>and here's the console output:</p> <pre><code>Edges: 948464 Fibonacci Dijkstra took 340 ms Min dist from 0 to 2 = 89.0 : 0 -&gt; 195 -&gt; 5523 -&gt; 5504 -&gt; 5870 -&gt; 5835 -&gt; 3076 -&gt; 15319 -&gt; 5588 -&gt; 5911 -&gt; 2 Binary Dijkstra took 302292 ms Min dist from 0 to 2 = 89.0 : 0 -&gt; 195 -&gt; 5523 -&gt; 5504 -&gt; 5870 -&gt; 5835 -&gt; 3076 -&gt; 15319 -&gt; 5588 -&gt; 5911 -&gt; 2 Simple Dijkstra took 0 ms Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 at java.util.ArrayList.rangeCheck(ArrayList.java:571) at java.util.ArrayList.get(ArrayList.java:349) at Dijkstra.print_path(Dijkstra.java:115) at Dijkstra.&lt;init&gt;(Dijkstra.java:25) at Router.main(Router.java:33) </code></pre>
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    1. COwas there an exception raised? if yes can you post that too pls?
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    2. COwhat is "p" in your main?
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    3. COoops, forgot to get rid of that before I pasted it here. The 'p' is a PrintStream variable (code not above). I am logging the algorithm running times into a txt file for future use.
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