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Java - count duplicates in ArrayList
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In this article, we would like to show you how to count duplicated elements in ArrayList in Java.
Quick solution:
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int occurrences = Collections.frequency(myArrayList, element);
In this example, we count the number of duplicated elements in letters ArrayList using Collections.frequency() method.
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import java.util.*;2
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public class Example {4
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public static void main(String[] args) {6
List<String> letters = new ArrayList<>();7
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letters.add("A");9
letters.add("A");10
letters.add("A");11
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letters.add("B");13
letters.add("B");14
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letters.add("C");16
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int occurrencesA = Collections.frequency(letters, "A");18
System.out.println("number of A element occurrences: " + occurrencesA);19
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int occurrencesB = Collections.frequency(letters, "B");21
System.out.println("number of B element occurrences: " + occurrencesB);22
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int occurrencesC = Collections.frequency(letters, "C");24
System.out.println("number of C element occurrences: " + occurrencesC);25
}26
}Output:
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number of A element occurrences: 32
number of B element occurrences: 23
number of C element occurrences: 1