Remove all elements from the ArrayList in Java

Prerequisite: ArrayList in Java

Given an ArrayList, the task is to remove all elements of the ArrayList in Java.

Examples:

Input: ArrayList = [1, 2, 3, 4] 
Output: ArrayList = [] 

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

• Using clear() method:

  Syntax:

  collection_name.clear();

  Code of clear() method:

  public void clear() {
      for (int i = 0; i < size; i++)
          list[i] = null;
  
      size = 0;
  }
  

  Below is the implementation of the above approach:

  
  

  
  
  

  // Java Program for remove all elements ArrayList // Using clear() method    // import  ArrayList package import java.util.ArrayList;    public class GFG {        // main method     public static void main(String[] args)     {         // create empty ArrayList         ArrayList<String> list = new ArrayList<>();            // Adding elements of list         list.add("Geeks");         list.add("for");         list.add("Geeks");         list.add("Gaurav");            // printing initial value ArrayList         System.out.println("ArrayList: " + list);            // print size of ArrayList         System.out.println("Size of ArrayList = "                            + list.size());            // remove all elements using clear() method         list.clear();            // printing ArrayList         System.out.println("\nAfter clear\n\n"                          + "ArrayList: " + list);            // print size of ArrayList after clear list         System.out.println("Size of ArrayList = "                            + list.size());     } }
  Output:

  ArrayList: [Geeks, for, Geeks, Gaurav]
  Size of ArrayList = 4
  
  After clear
  
  ArrayList: []
  Size of ArrayList = 0
  

  Time Complexity: O(N)

• Using removeAll() method

  Syntax:

  collection_name.removeAll(collection_name);

  Code of removeAll() method:

  public boolean removeAll(Collection list) {
      boolean isModi = false;
      Iterator ite= iterator();
      while (ite.hasNext()) {
          if (list.contains(ite.next())) {
              ite.remove();
              isModi = true;
          }
      }
      return isModi;
  }
  

  Below is the implementation of the above approach:

  
  

  
  
  

  // Java Program for remove all elements ArrayList // Using removeAll() method    // import  ArrayList package import java.util.ArrayList;    public class GFG {        // main method     public static void main(String[] args)     {         // create empty ArrayList         ArrayList<String> list = new ArrayList<>();            // Adding elements of list         list.add("Geeks");         list.add("for");         list.add("Geeks");         list.add("Gaurav");            // printing initial value ArrayList         System.out.println("ArrayList: " + list);            // print size of ArrayList         System.out.println("Size of ArrayList = "                            + list.size());            // remove all elements using clear() method         list.removeAll(list);            // printing ArrayList         System.out.println("\nAfter clear\n\n"                          + "ArrayList: " + list);            // print size of ArrayList after clear list         System.out.println("Size of ArrayList = "                            + list.size());     } }
  Output:

  ArrayList: [Geeks, for, Geeks, Gaurav]
  Size of ArrayList = 4
  
  After clear
  
  ArrayList: []
  Size of ArrayList = 0
  

  Time Complexity: O(N^2)