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POJava - How to find count of items in a list in another list
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  1. POJava - How to find count of items in a list in another list
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    copied!<p>Say I have two lists:</p> <pre><code>List&lt;String&gt;products = new ArrayList&lt;String&gt;(); products.add("computer"); products.add("phone"); products.add("mouse"); products.add("keyboard"); List&lt;String&gt;cart = new ArrayList&lt;String&gt;(); cart.add("phone"); cart.add("monitor"); </code></pre> <p>I need to find how many items in the cart list exist in the products list. For the lists above, the answer would be 1 (as phone is in products and cart). If the cart list was:</p> <pre><code>List&lt;String&gt;cart = new ArrayList&lt;String&gt;(); cart.add("desk"); cart.add("chair"); </code></pre> <p>The result would be 0. If cart contained computer, mouse, desk, chair, the result would be 2 (for computer and mouse).</p> <p>Is there something in the <a href="http://commons.apache.org/collections/userguide.html" rel="nofollow noreferrer">Apache Commons Collections</a> or the <a href="http://code.google.com/p/google-collections/" rel="nofollow noreferrer">Google Collections API</a>? I've looked through them and see ways to get a bag count, but not from another list, although it's possible I'm missing something. Right now, the only way I can think of is to iterate over the cart items and see if products <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#contains(java.lang.Object)" rel="nofollow noreferrer">contains</a> the individual item and keep a count. I can't use <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html#containsAll(java.util.Collection)" rel="nofollow noreferrer">containsAll</a> as I need the count (not a boolean), and that would fail if all items in cart didn't exist in the product list (which can happen).</p> <p>I'm using Java 1.6 if that matters.</p>
 

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