Frequent question: How do you remove duplicates in Java?

How do you remove duplicates from a list in Java?

Given an ArrayList with duplicate values, the task is to remove the duplicate values from this ArrayList in Java.


  1. Get the ArrayList with duplicate values.
  2. Create a new List from this ArrayList.
  3. Using Stream(). distinct() method which return distinct object stream.
  4. convert this object stream into List.

How do I remove duplicates from a list?

To remove the duplicates from a list, you can make use of the built-in function set(). The specialty of the set() method is that it returns distinct elements. You can remove duplicates from the given list by importing OrderedDictfrom collections.

How do you remove duplicate characters in a string in Java?

1) By using for loop

  1. In the first step, we have to convert the string into a character array.
  2. Calculate the size of the array.
  3. Call removeDuplicates() method by passing the character array and the length.
  4. Traverse all the characters present in the character array.
  5. Check whether the str[i] is present before or not.
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How do I remove duplicates from a list in Java 8?

Remove duplicates in arraylist – Java 8

Use steam’s distinct() method which returns a stream consisting of the distinct elements comparing by object’s equals() method. Collect all district elements as List using Collectors. toList() . Java program to remove duplicates from arraylist in java without using Set.

Can ArrayList have duplicates?

Duplicates : ArrayList allows duplicate values while HashSet doesn’t allow duplicates values. Ordering : ArrayList maintains the order of the object in which they are inserted while HashSet is an unordered collection and doesn’t maintain any order.

Does linked list allow duplicates?

A LinkedList can store the data by use of the doubly Linked list. Each element is stored as a node. The LinkedList can have duplicate elements because of each value store as a node. But there may be a situation when we want to store only unique elements in LinkedList and want to remove duplicates from linked list.

Does HashSet allow duplicates?

Duplicates: HashSet doesn’t allow duplicate values. HashMap stores key, value pairs and it does not allow duplicate keys.

How HashSet remove duplicates from a list?

The easiest way to remove repeated elements is to add the contents to a Set (which will not allow duplicates) and then add the Set back to the ArrayList : Set<String> set = new HashSet<>(yourList); yourList. clear(); yourList.

How do you remove duplicates from a linked list in Java?

Write a removeDuplicates() function that takes a list and deletes any duplicate nodes from the list. The list is not sorted. For example if the linked list is 12->11->12->21->41->43->21 then removeDuplicates() should convert the list to 12->11->21->41->43.

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How do you remove duplicates from a string in Java without using collections?

Remove duplicates from arraylist without using collections

  1. package arrayListRemoveduplicateElements;
  2. import java.util.ArrayList;
  3. public class RemoveDuplicates {
  4. public static void main(String[] args){
  5. ArrayList<Object> al = new ArrayList<Object>();
  6. al.add(“java”);
  7. al.add(‘a’);
  8. al.add(‘b’);

How do you find duplicates in a string in Java?


  1. public class DuplicateCharacters {
  2. public static void main(String[] args) {
  3. String string1 = “Great responsibility”;
  4. int count;
  5. //Converts given string into character array.
  6. char string[] = string1.toCharArray();
  7. System.out.println(“Duplicate characters in a given string: “);

What is indexOf method in Java?

The Java indexOf() method finds the index position at which a specified string begins. This method lets you find a string within another string. … indexOf() returns the index of a particular character or substring in a string.

How do you remove duplicates from a HashSet in Java?

Set implementations in Java has only unique elements. Therefore, it can be used to remove duplicate elements. HashSet<Integer>set = new HashSet<Integer>(list1); List<Integer>list2 = new ArrayList<Integer>(set);

How do I find duplicates in a HashMap?

How do you find duplicate characters in a string?

  1. import java.util.HashMap;
  2. import java.util.Map;
  3. import java.util.Set;
  4. public class DuplicateCharFinder {
  5. public void findIt(String str) {
  6. Map<Character, Integer> baseMap = new HashMap<Character, Integer>();
  7. char[] charArray = str.toCharArray();

How do I remove duplicates from ArrayList in Kotlin?

Remove duplicate elements from a list in Kotlin

  1. Using Set. The idea is to convert the given list to a set collection. …
  2. Using distinct() function. To preserve the original order, you can also use the distinct() function, as shown below: