How to Count Element Occurrences in a Java ArrayList?

Counting Element Occurrences in ArrayList

The Java Collection framework provides numerous utilities for manipulating and querying collections. One common task is determining the count of specific elements within a collection. This article explores how to count element occurrences in an ArrayList using the Collections API.

Querying ArrayList Element Count

For the ArrayList in the question:

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

The objective is to count the number of occurrences of the element "bat."

Collections.frequency() API

The Collections class offers a static method called frequency() that returns the count of an element within a collection. This method accepts two parameters, the collection and the element to search for.

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

The method will return the count of the element in the collection. In this case, it will return 3, as the ArrayList contains three elements equal to "bat."

This method is available in Java Development Kit (JDK) 1.6 and higher, making it compatible with the product requirements specified in the question.

Conclusion

The Collections.frequency() method provides a straightforward solution for counting the number of occurrences of an element in an ArrayList. This API is simple to use and efficient, offering an effective method for working with collections in Java.

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