Remove all Occurrences of an Element from Array in Java (original) (raw)

Last Updated : 01 May, 2025

In Java, removing all occurences of a given element from an array can be done using different approaches that are,

Naive approach using array copy
Java 8 Streams
Using ArrayList.removeAll()
Using List.removeIf()

**Problem Stament: Given an **array and a **key, the task is to **remove all occurrences of the specified key from the array in Java.

**Examples to Remove Elements Occurrences in Array:

**Input: array = { 3, 9, 2, 3, 1, 7, 2, 3, 5 }, key = 3
**Output: [9, 2, 1, 7, 2, 5]

**Input: array = { 10, 20, 10, 30, 50, 10 }, key = 10
**Output: [20, 30, 50]

**Illustration: In this example, we will remove all occurrences of an element from an array using the Arrays.copyOf method.

Java `

// Java program remove all occurrences // of an element from Array using naive method import java.util.Arrays;

class Geeks {

// function to remove all occurrences 
// of an element from an array 
public static int[] removeElements(int[] a, int k) 
{ 
    // Move all other elements to beginning 
    int ind = 0; 
    
    for (int i=0; i<a.length; i++) 
        if (a[i] != k) 
            a[ind++] = a[i]; 

    // Create a copy of arr[] 
    return Arrays.copyOf(a, ind); 
} 

// Driver code 
public static void main(String[] args) 
{ 
    int[] a = { 3, 9, 2, 3, 1, 7, 2, 3, 5 }; 
    int k = 3; 
    a = removeElements(a, k); 
    System.out.println(Arrays.toString(a)); 
}

}

**Complexity of the above method:

**Time Complexity: O(n)
**Space Complexity: O(n)

Java Program to Remove All Occurrences of an Element from Array

1. Using Java 8 Stream

**Approach:

Get the array and the key.
Filter all elements of the list which is equal to a given key
Convert the list back to an array and return it.

**Illustration: Here, we will use the Java 8 streams to remove all occurrences of an element from an array.

Java `

// Java program remove all occurrences // of an element from Array using Stream import java.util.Arrays;

public class Geeks { public static void main(String[] args) {

    // Example array
    Integer[] a = { 3, 9, 2, 3, 1, 7, 2, 3, 5 }; 

    // Element to be removed
    int k = 3;

    // Remove all occurrences of the element using Java 8 Stream
    Integer[] ans = Arrays.stream(a)
    
            // Filter out the element to remove
            .filter(e -> e != k)  
            .toArray(Integer[]::new);           

    System.out.println(Arrays.toString(ans));
}

}

2. Using Java ArrayList

Approach:

Get the array and the key.
Create an empty ArrayList.
Insert all elements from the array into the list except the specified key
Convert the list back to an array and return it.

Alternative Approach:

First, create a List of arrays.
Remove all elements of the array into the list that are the specified key.
Convert the list back to an array and return it.

**Illustration: Using the ArrayList to remove all occurrences of an element from an array.

Java `

// Java program remove all occurrences // of an element from Array using ArrayList import java.util.ArrayList; import java.util.Arrays; import java.util.List;

// Driver Class public class Geeks {

  // Main Method
public static void main(String[] args) {
    
    Integer[] a = { 3, 9, 2, 3, 1, 7, 2, 3, 5 }; 

    // Element to be removed
    Integer k = 3;

    // Convert array to ArrayList
    List<Integer> l = new ArrayList<>(Arrays.asList(a));

    // Remove all occurrences of the element
    l.removeAll(Arrays.asList(k));

    // Convert ArrayList back to array
    Integer[] newArr = l.toArray(new Integer[0]);

    // Print the result
    System.out.println(Arrays.toString(newArr));
}

}

3. Using List.removeAll()

**Approach:

First, create a list from the array.
Insert all elements of the array into the list
Remove all elements that match the given key.
Convert the list back to an array and return it.

**Illustration: Using the List.removeAll() to remove all occurrences of an element from an array.

Java `

// Java program remove all occurrences // of an element from Array using List.removeAll import java.util.*;

// Driver Class public class Geeks { // Main Method public static void main(String[] args) {

    // Example array
    Integer[] a = { 3, 9, 2, 3, 1, 7, 2, 3, 5 };

    // Element to be removed
    Integer k = 3;

    // Convert array to List (using ArrayList to allow modification)
    List<Integer> l = new ArrayList<>(Arrays.asList(a));

    // Remove all occurrences of the element
    l.removeAll(Arrays.asList(k));

    // Convert List back to array
    Integer[] ans = l.toArray(new Integer[0]);

    // Print the result
    System.out.println(Arrays.toString(ans));
}

}

4. Using List.removeIf()

**Approach:

First Create an empty List of Array.
Insert all elements of the array into the list.
Remove all those elements which is you want to remove using the equals() method.
Convert the list back to an array and return it.

**Illustration: Using the List.removeIf() to remove all occurrences of an element from an array.

Java `

// Java program remove all occurrences // of an element from Array using removeIf() import java.util.*;

// Driver Class public class Geeks { // Main Method public static void main(String[] args) {

    // Example array
    Integer[] a = { 3, 9, 2, 3, 1, 7, 2, 3, 5 };

    // Element to be removed
    int k = 3;

    // Convert array to List (using ArrayList to allow modification)
    List<Integer> l = new ArrayList<>(Arrays.asList(a));

    // Remove all occurrences using removeIf()
    l.removeIf(e -> e == k);

    // Convert List back to array
    Integer[] ans = l.toArray(new Integer[0]);

    System.out.println(Arrays.toString(ans));
}

}