Remove repeated elements from ArrayList in Java

11 Dec, 2018
Prerequisite: ArrayList in Java
Given an ArrayList, the task is to remove repeated elements of the ArrayList in Java.
Examples:
Input: ArrayList = [1, 2, 2, 3, 4, 4, 4] 
Output: [1, 2, 3, 4] 

Input: ArrayList = [12, 23, 23, 34, 45, 45, 45, 45, 57, 67, 89] 
Output: [12, 23, 34, 45, 57, 67, 89]

Below are the various methods to remove repeated elements an ArrayList in Java:
Using a Set: Since Set is a collection which do not includes any duplicate elements. Hence the solution can be achieved with the help of a Set.Approach:Get the ArrayList with repeated elements.Convert the ArrayList to Set.Now convert the Set back to ArrayList. This will remove all the repeated elements.Below is the implementation of the above approach:// Java code to illustrate remove duolicate// of ArrayList using hashSet<> method  import java.util.*;  public class GFG {    public static void main(String args[])    {          // create a ArrayList String type        ArrayList<String>            gfg = new ArrayList<String>();          // Initialize an ArrayList        gfg.add("Geeks");        gfg.add("for");        gfg.add("Geeks");          // print ArrayList        System.out.println("Original ArrayList : "                           + gfg);          // -----Using LinkedHashSet-----        System.out.println("\nUsing LinkedHashSet:\n");          // create a set and copy all value of list        Set<String> set = new LinkedHashSet<>(gfg);          // create a list and copy all value of set        List<String> gfg1 = new ArrayList<>(set);          // print ArrayList        System.out.println("Modified ArrayList : "                           + gfg1);          // -----Using HashSet-----        System.out.println("\nUsing HashSet:\n");          // create a set and copy all value of list        Set<String> set1 = new HashSet<>(gfg);          // create a list and copy all value of set        List<String> gfg2 = new ArrayList<>(set);          // print ArrayList        System.out.println("Modified ArrayList : "                           + gfg2);    }}Output:Original ArrayList : [Geeks, for, Geeks]

Using LinkedHashSet:

Modified ArrayList : [Geeks, for]

Using HashSet:

Modified ArrayList : [Geeks, for]

Approach:
Get the ArrayList with repeated elements.Convert the ArrayList to Set.Now convert the Set back to ArrayList. This will remove all the repeated elements.
Get the ArrayList with repeated elements.
Convert the ArrayList to Set.
Now convert the Set back to ArrayList. This will remove all the repeated elements.
Below is the implementation of the above approach:
// Java code to illustrate remove duolicate// of ArrayList using hashSet<> method  import java.util.*;  public class GFG {    public static void main(String args[])    {          // create a ArrayList String type        ArrayList<String>            gfg = new ArrayList<String>();          // Initialize an ArrayList        gfg.add("Geeks");        gfg.add("for");        gfg.add("Geeks");          // print ArrayList        System.out.println("Original ArrayList : "                           + gfg);          // -----Using LinkedHashSet-----        System.out.println("\nUsing LinkedHashSet:\n");          // create a set and copy all value of list        Set<String> set = new LinkedHashSet<>(gfg);          // create a list and copy all value of set        List<String> gfg1 = new ArrayList<>(set);          // print ArrayList        System.out.println("Modified ArrayList : "                           + gfg1);          // -----Using HashSet-----        System.out.println("\nUsing HashSet:\n");          // create a set and copy all value of list        Set<String> set1 = new HashSet<>(gfg);          // create a list and copy all value of set        List<String> gfg2 = new ArrayList<>(set);          // print ArrayList        System.out.println("Modified ArrayList : "                           + gfg2);    }}
Original ArrayList : [Geeks, for, Geeks]

Using LinkedHashSet:

Modified ArrayList : [Geeks, for]

Using HashSet:

Modified ArrayList : [Geeks, for]

Using Java 8 Lambdas:Approach:Get the ArrayList with repeated elements.Convert the ArrayList to Stream using stream() method.Set the filter condition to be distinct using distinct() method.Collect the filtered values as List using collect() method. This list will be with repeated elements removedBelow is the implementation of the above approach:Example:// Java code to illustrate remove duolicate// of ArrayList using hashSet<> method  import java.util.*;import java.util.stream.Collectors;  public class GFG {    public static void main(String args[])    {        // create a ArrayList String type        ArrayList<String>            gfg = new ArrayList<String>();          // Initialize an ArrayList        gfg.add("Geeks");        gfg.add("for");        gfg.add("Geeks");          // print ArrayList        System.out.println("Original ArrayList : "                           + gfg);          // create a list and copy all distinct value of list        List<String> gfg1 = gfg.stream()                                .distinct()                                .collect(Collectors.toList());          // print modified list        System.out.println("Modified List : " + gfg1);    }}Output:Original ArrayList : [Geeks, for, Geeks]
Modified List : [Geeks, for]

Approach:
Get the ArrayList with repeated elements.Convert the ArrayList to Stream using stream() method.Set the filter condition to be distinct using distinct() method.Collect the filtered values as List using collect() method. This list will be with repeated elements removed
Get the ArrayList with repeated elements.
Convert the ArrayList to Stream using stream() method.
Set the filter condition to be distinct using distinct() method.
Collect the filtered values as List using collect() method. This list will be with repeated elements removed
Below is the implementation of the above approach:
Example:
// Java code to illustrate remove duolicate// of ArrayList using hashSet<> method  import java.util.*;import java.util.stream.Collectors;  public class GFG {    public static void main(String args[])    {        // create a ArrayList String type        ArrayList<String>            gfg = new ArrayList<String>();          // Initialize an ArrayList        gfg.add("Geeks");        gfg.add("for");        gfg.add("Geeks");          // print ArrayList        System.out.println("Original ArrayList : "                           + gfg);          // create a list and copy all distinct value of list        List<String> gfg1 = gfg.stream()                                .distinct()                                .collect(Collectors.toList());          // print modified list        System.out.println("Modified List : " + gfg1);    }}
Original ArrayList : [Geeks, for, Geeks]
Modified List : [Geeks, for]

Java-ArrayList
Java-Collections
java-hashset
java-lambda
Java-List-Programs
Technical Scripter 2018
Java
Technical Scripter
Java
Java-Collections
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