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Sorting an ArrayList
this example from a Well House Consultants training course
Source code: Aileen.java Module: J050
import java.io.*;
import java.util.*; /* Example Zoe expanded to sort and report on all the objects loaded from the file. We have: 1. Set the class to implement "Comparable" which means that we have added a compareTo method which returns an integer (-ve, 0, +ve) 2. Called Collections.Sort on the ArrayList object (Collections.Sort is a static method of the Collection object type in java.util) 3. Provided a toString method so that we can easily display an Aileen object. 4. Looped through our ArrayList after sorting in to output all the members in it. */ public class Aileen implements Comparable { private String Host; private String Request; private String Time; private int status; public static void main (String [] args) throws IOException { ArrayList<Aileen> Visits = new ArrayList<Aileen>(); File Source = new File("access_log.xyz"); BufferedReader DataInput = new BufferedReader(new FileReader(Source)); while (true) { String stuff = DataInput.readLine(); if (stuff == null) break; try { Aileen wham = new Aileen(stuff); Visits.add(wham); } catch (Exception e) { } } System.out.println ("Objects have I "+ Visits.size()); /* Add some sorting and output */ /* Using the comparable interface - it will sort the objects in the default way for sorting "Aileen"s */ Collections.sort(Visits); /* The print them out in order */ for (int k=0; k<Visits.size(); k++) { System.out.println(Visits.get(k)); } } public Aileen(String stuff) throws Exception{ try { StringTokenizer Chunk = new StringTokenizer(stuff," "); Host = Chunk.nextToken(); String skip = Chunk.nextToken(); skip = Chunk.nextToken("["); Time = Chunk.nextToken(" \t"); skip = Chunk.nextToken("\""); Request = Chunk.nextToken(); skip = Chunk.nextToken(" \t"); status = Integer.parseInt(Chunk.nextToken(" \t")); } catch (Exception e) { System.out.println("Short line"); throw e; } } /* Default sort is by status number .... If statuses are the same, sort by Host name */ public int compareTo(Object that) { // Can we differentiate by status? int newstate = this.status - ((Aileen)that).status; if (newstate != 0) return newstate; // If we can't, differentiate on host name return (this.Host.compareTo(((Aileen)that).Host)); } public String toString() { String rezult = Host + " " + /* Request + " " + */ Time + " " + status; return rezult; } } /* ------------------- Sample Output Dorothy-2:java grahamellis$ java Aileen | more Short line Short line Short line Short line Short line Short line Short line Short line Objects have I 6904 aviemore [15/Jul/1998:08:32:55 200 aviemore [15/Jul/1998:08:35:52 200 aviemore [15/Jul/1998:08:38:14 200 aviemore [21/Jul/1998:12:01:12 200 aviemore [22/Jul/1998:05:54:39 200 aviemore [22/Jul/1998:06:08:02 200 aviemore [22/Jul/1998:06:08:11 200 [snip - 6800+ lines!] whale [11/Sep/1998:08:37:39 500 whale [11/Sep/1998:09:24:24 500 whale [11/Sep/1998:09:26:36 500 whale [11/Sep/1998:09:30:23 500 whale [11/Sep/1998:09:32:08 500 catfish [28/Aug/1998:09:59:41 501 tuna [23/Oct/1998:05:19:34 501 Dorothy-2:java grahamellis$ */ Learn about this subject
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