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Join two ArrayLists in Java

  • Difficulty Level : Easy
  • Last Updated : 11 Dec, 2018

Given two ArrayLists in Java, the task is to join these ArrayLists.

Examples:

Input: ArrayList1: [Geeks, For, ForGeeks], ArrayList2: [GeeksForGeeks, A computer portal]
Output: ArrayList: [Geeks, For, ForGeeks, GeeksForGeeks, A computer portal]

Input: ArrayList1: [G, e, e, k, s], ArrayList2: [F, o, r, G, e, e, k, s]
Output: ArrayList: [G, e, e, k, s, F, o, r, G, e, e, k, s]

Approach: ArrayLists can be joined in Java with the help of Collection.addAll() method. This method is called by the destination ArrayList and the other ArrayList is passed as the parameter to this method. This method appends the second ArrayList to the end of the first ArrayList.



Syntax:

ArrayList1.addAll(ArrayList2);

Below is the implementation of the above approach:




// Java program to demonstrate
// How to sort ArrayList in descending order
  
import java.util.*;
  
public class GFG {
    public static void main(String args[])
    {
  
        // Get the ArrayList1
        ArrayList<String>
            list1 = new ArrayList<String>();
  
        // Populate the ArrayList
        list1.add("Geeks");
        list1.add("For");
        list1.add("ForGeeks");
  
        // Print the ArrayList 1
        System.out.println("ArrayList 1: "
                           + list1);
  
        // Get the ArrayList2
        ArrayList<String>
            list2 = new ArrayList<String>();
  
        list2.add("GeeksForGeeks");
        list2.add("A computer portal");
  
        // Print the ArrayList 2
        System.out.println("ArrayList 2: "
                           + list2);
  
        // Join the ArrayLists
        // using Collection.addAll() method
        list1.addAll(list2);
  
        // Print the joined ArrayList
        System.out.println("Joined ArrayLists: "
                           + list1);
    }
}

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