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    <p>First of all, something like is wrong:</p> <pre><code>Vector&lt;String&gt; set = new &lt;String&gt;Vector(); </code></pre> <p>The correct syntax is this:</p> <pre><code>Vector&lt;String&gt; set = new Vector&lt;String&gt;(); </code></pre> <p>Second of all, if you do something like this:</p> <pre><code>Vector&lt;String&gt; set1,set2,set3,set4,set5 = new Vector&lt;String&gt;(); </code></pre> <p>...only <code>set5</code> will be initialized. Each variable must be initialized independently. You <em>could</em> do something like this:</p> <pre><code>Vector&lt;String&gt; set1,set2,set3,set4,set5; set1 = set2 = set3 = set4 = set5 = new Vector&lt;String&gt;(); </code></pre> <p>...but then all of the variables would point to the same <code>Vector</code>, and modifications to one variable would affect all the others. You'll have to initialize each variable separately.</p> <p>Third, doing this:</p> <pre><code>candidatesSet = null; </code></pre> <p>...does nothing if <code>candidatesSet</code> is not initialized yet, since non-primitive instance variables are initialized to null anyway. That's your problem, you're calling <code>.add(String)</code> on a null object, which cases a <code>NullPointerException</code>.</p> <p>Fixing those issues will make your code work, but there's one last problem. <code>Vector</code> is a somewhat outdated class, and it has been replaced by the Java Collections API. Try using <a href="http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html" rel="nofollow"><code>ArrayList</code></a> instead of <code>Vector</code>, like so:</p> <pre><code>List&lt;String&gt; candidatesSet = new ArrayList&lt;String&gt;(); </code></pre> <p>This will make your code more efficient and less archaic.</p>
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    1. COThanks that worked :) Also i was thinking that vector is a better class than ArrayList(used it earlier)
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