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Java Program to Add the Data from the Specified Collection in the Current Collection

  • Last Updated : 05 Oct, 2021

The grouping of objects in a single unit is called a collection. For example Array, Lists, Hashsets, etc.  Data can be added from a specified collection in the current collection by using the addAll() method in Java. This method falls under the header file, java.util.*.  The addAll() method returns a true value if the adding of the collection is successful after calling the method else it returns a false value.

We can use the addAll() method in two ways namely:

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  • The static method
  • The instance method

Let there be 2 lists.

The static method Declaration



Collections.addAll(List1,List2)

The instance method Declaration

Let the index where List2 needs to be inserted in List1 is 1.

List1.addAll(1, List2);

The addAll() method always throws the following exceptions:

  • NullPointerException: This exception is thrown if the specified or the current collection has null values.
  • IllegalArgumentException: If the arguments of the specified collection have values that prevent them from being added to the current collection, this exception is thrown.

Example 1:

Input: boolean b = List1.addAll(large,extra-large)

If the appending is successful
Output: true 

If the appending is unsuccessful
Output: false

Example 2:

Input:  Collections.addAll(List1,List2)
Output: List1 = [small,medium,large,extra-large]

Approach used:

  • Initializing the two collections.
  • Using the addAll() method to append the lists.
  • Checking the boolean value of the method call.
  • Printing the collections’ final values.

Below is the implementation of the above approach:

Java




// Java Program to Add the Data from the Specified
// Collection in the Current Collection
 
import java.util.*;
public class AddCollections {
    public static void main(String[] args)
    {
        // Creating object of a list which is our current
        // collection
        ArrayList<Integer> list = new ArrayList<Integer>();
 
        // Adding values to the initial list
        list.add(1);
        list.add(2);
        list.add(3);
 
        // Printing the initial list
        System.out.println(
            "Initial collection value of list: " + list);
 
        // creating object of the specified list.
        ArrayList<Integer> list2 = new ArrayList<Integer>();
 
        list2.add(4);
        list2.add(5);
        list2.add(6);
 
        // Printing the initial list
        System.out.println(
            "Initial collection value of list2: " + list2);
 
        // returns true if addition is successful else
        // false
        // adding data from the specified collection in
        // the  current collection at a specified position
        boolean b = list.addAll(2, list2);
 
        // printing the boolean result
        System.out.println("Boolean Result: " + b);
 
        // printing the final list with the new values added
        System.out.println(
            "Final collection value of list: " + list);
 
        // creating an object for a different collection
 
        Integer[] arr = new Integer[4];
 
        // Initializing the array
        arr[0] = 9;
        arr[1] = 8;
        arr[2] = 7;
        arr[3] = 6;
 
        // Adding array elements to list2
        Collections.addAll(list2, arr);
 
        // Printing the new List2
        System.out.println(
            "Final collection value of list2: " + list2);
    }
}
Output
Initial collection value of list: [1, 2, 3]
Initial collection value of list2: [4, 5, 6]
Boolean Result: true
Final collection value of list: [1, 2, 4, 5, 6, 3]
Final collection value of list2: [4, 5, 6, 9, 8, 7, 6]



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