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    <p>If you have no problems with using the standard library (always preferable, why reinvent the wheel) try</p> <pre><code>List&lt;String&gt; uniques = new ArrayList&lt;String&gt;(new HashSet&lt;String&gt;(oldList)); </code></pre> <p>The <code>HashSet</code> will only contain unique strings and the <code>ArrayList</code> constructor takes any <code>Collection</code> (including a <code>HashSet</code>) to build a list from.</p> <p>Judging from your comments it seems like you are trying to implement an <a href="http://en.wikipedia.org/wiki/Associative_array" rel="nofollow">Associative Array</a> with unique keys using an ArrayList. The better approach is to use a <a href="http://docs.oracle.com/javase/7/docs/api/java/util/Map.html" rel="nofollow">Map</a> implementation like HashMap to pair IDs with their associated Strings.</p> <pre><code>Map&lt;Integer, String&gt; map = new HashMap&lt;&gt;(); map.put(1, "This string corresponds to ID=1"); map.put(3, "Donald Ducks Nephews"); map.put(7, "Is a Prime"); </code></pre> <p>Then to get a value associated with an ID:</p> <pre><code>int key = someObject.getID(); String value = map.get(key); </code></pre> <p>All the Map implementations use unique keys so there is no need for you to check for redundant IDs, if you try to add a new (key,value) pair the value associated with the ID will be replaced if the map contains the key.</p> <pre><code>map.put(1, "New String"); String s = map.get(1); //s will no longer be "This string corresponds to ID=1" </code></pre> <p>If you don't want this behavior you have the choice of either subclassing one of the Map implementations to ignore <code>.put(key, value)</code> if the map contains <code>key,value</code> or delegating <code>.put(key,value)</code> to some other class.</p> <p><strong>Subclassing:</strong></p> <pre><code>public class UniqueValueHashMap&lt;K,V&gt; extends HashMap&lt;K, V&gt;{ @Override public V put(K key, V value) { if (containsKey(key)) return null; return super.put(key, value); } </code></pre> <p><strong>Delegating</strong></p> <pre><code> public class SomeClass { private Map&lt;Integer, String&gt; map = new HashMap&lt;&gt;(); // ...stuff this class does public String put(int key, String value) { if (map.containsKey(key)) return null; return map.put(key, value); } // ...more stuff this class does } </code></pre> <p>Delegation is the better approach, notice how you can change the map implementation (using maybe a TreeMap instead of HashMap) without introducing a new class where you override the <code>.put(key,value)</code> of TreeMap.</p>
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    1. COThanks for your reply @arynaq . This doesn't work exactly as I need because in the arrayList I've got strings formatted as `("ID,String")` and that's why I am using `ChopMD()` to return a string without the ID in order to compare.
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