Remove duplicate object in list java

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 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 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 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 stream = numbers.stream[]; // call the distinct[] of Stream // to remove duplicate elements stream = stream.distinct[]; // convert the stream to arraylist numbers = [ArrayList]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.