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:
- 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 Collectionimport 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]