How to Efficiently Count Element Occurrences in a Java ArrayList?

Counting Occurrences of Elements in Lists: A Java Solution

In Java's ArrayList implementation, a collection class, counting the number of occurrences of specific elements can be crucial. Consider the example below:

ArrayList<String> animals = new ArrayList<String>();
animals.add("bat");
animals.add("owl");
animals.add("bat");
animals.add("bat");

Here, the animals ArrayList includes three occurrences of "bat" and one of "owl." This raises the question of how to determine the count of "bat" occurrences in the ArrayList without relying on Google's Collection Multiset, which is not compatible with JDK 1.6.

Solution:

The Java Collections framework provides a concise solution for this scenario through its static frequency method:

int occurrences = Collections.frequency(animals, "bat");

Utilizing this method, we can effortlessly ascertain the number of occurrences for any desired element within the ArrayList. In this specific example, the result stored in occurrences would be 3. The Collections.frequency method proves to be a versatile tool for this common programming task.

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