How to count duplicate elements in ArrayList?

Question

I need to separate and count how many values in arraylist are the same and print them according to the number of occurrences.

I\'ve got an arraylist called digits :<

Answer 1

By using the Stream API for example.

package tests;

import org.junit.Assert;
import org.junit.Test;

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

public class Duplicates {

    @Test
    public void duplicates() throws Exception {
        List items = Arrays.asList(1, 1, 2, 2, 2, 2);

        Map result = items.stream()
                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

        Assert.assertEquals(Long.valueOf(2), result.get(1));
        Assert.assertEquals(Long.valueOf(4), result.get(2));
    }
}