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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.*;
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public class Example {
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public static void main(String[] args) {
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List<String> letters = new ArrayList<>();
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letters.add("A");
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letters.add("A");
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letters.add("A");
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letters.add("B");
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letters.add("B");
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letters.add("C");
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int occurrencesA = Collections.frequency(letters, "A");
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System.out.println("number of A element occurrences: " + occurrencesA);
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int occurrencesB = Collections.frequency(letters, "B");
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System.out.println("number of B element occurrences: " + occurrencesB);
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int occurrencesC = Collections.frequency(letters, "C");
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System.out.println("number of C element occurrences: " + occurrencesC);
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}
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}
Output:
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number of A element occurrences: 3
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number of B element occurrences: 2
3
number of C element occurrences: 1