Example 1: Remove duplicate elements from ArrayList using Set
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedHashSet;
import java.util.Set;
class Main {
public static void main(String[] args) {
// create an arraylist from the array
// using asList() method of the Arrays class
ArrayList<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 1, 3));
System.out.println("ArrayList with duplicate elements: " + numbers);
// convert the arraylist into a set
Set<Integer> set = new LinkedHashSet<>();
set.addAll(numbers);
// delete al elements of arraylist
numbers.clear();
// add element from set to arraylist
numbers.addAll(set);
System.out.println("ArrayList without duplicate elements: " + numbers);
}
}
Output
ArrayList with duplicate elements: [1, 2, 3, 4, 1, 3] ArrayList without duplicate elements: [1, 2, 3, 4]
In the above example, we have created an arraylist named numbers. The arraylist contains duplicate elements.
To remove duplicate elements from the arraylist, we have
- add all elements from arraylist to set
- empty the arraylist using clear() method
- add all elements from set to arraylist
Here, we have used the LinkedHashSet
to create a set. It is because it removes the duplicate elements and maintains insertion order. To learn more, visit Java LinkedHashSet.
Example 2: Remove duplicate elements from ArrayList using Stream
import java.util.ArrayList;
import java.util.Arrays;
import java.util.stream.Collectors;
import java.util.stream.Stream;
class Main {
public static void main(String[] args) {
// create an arraylist from the array
// using asList() method of the Arrays class
ArrayList<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 1, 3));
System.out.println("ArrayList with duplicate elements: " + numbers);
// create a stream from arraylist
Stream<Integer> stream = numbers.stream();
// call the distinct() of Stream
// to remove duplicate elements
stream = stream.distinct();
// convert the stream to arraylist
numbers = (ArrayList<Integer>)stream.collect(Collectors.toList());
System.out.println("ArrayList without duplicate elements: " + numbers);
}
}
Output
ArrayList with duplicate elements: [1, 2, 3, 4, 1, 3] ArrayList without duplicate elements: [1, 2, 3, 4]
In the above example, we have created an arraylist named numbers. The arraylist contains duplicate elements.
Here, we have used the Stream class to remove duplicate elements from the arraylist.
- numbers.stream() - create a stream from the arraylist
- stream.distinct() - removes duplicate elements
- stream.collect(Collectors.toList()) - returns a list from the stream
Here, we have used typecasting to convert the returned list into an arraylist.