In this article, we will discuss how to create ArrayList using Collections class’s utility nCopies() method
This is used to create ArrayList containing multiple copies of same elements or say same objects
Creating ArrayList using nCopies method :
Method signature:
public static List nCopies(int n, Object object);
Where,
- n – number of copies to be created
- object – element value (or object for which multiple copies required)
CreateArrayListUsingNCopies.java
package in.bench.resources.java.collections; import java.util.ArrayList; import java.util.Collections; public class CreateArrayListUsingNCopies { public static void main(String[] args) { // 7 copies of String object ArrayList<String> lstString = new ArrayList<String>( Collections.nCopies(7, "BRN")); // printing List of String object System.out.println("ArrayList of String objects : " + lstString); // create a customer object Customer cust = new Customer(101, "Berry"); // 3 copies of Customer object - user-defined object ArrayList<Customer> lstCustomer = new ArrayList<Customer>( Collections.nCopies(3, cust)); // printing List of Customer object System.out.println("\n\nArrayList of Customer objects : " + lstCustomer); } } class Customer { // member variables int custId; String custName; // 2-arg constructors public Customer(int custId, String custName) { super(); this.custId = custId; this.custName = custName; } // overriding toString method @Override public String toString() { return "\nCustomer [" + "Id=" + custId + ", Name=" + custName + "]"; } }
Output:
ArrayList of String objects : [BRN, BRN, BRN, BRN, BRN, BRN, BRN] ArrayList of Customer objects : [ Customer [Id=101, Name=Berry], Customer [Id=101, Name=Berry], Customer [Id=101, Name=Berry]]
References:
- https://docs.oracle.com/javase/tutorial/collections/intro/
- https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
- https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html
- https://docs.oracle.com/javase/tutorial/collections/interfaces/list.html
- https://docs.oracle.com/javase/7/docs/api/java/util/List.html
- https://docs.oracle.com/javase/tutorial/collections/interfaces/order.html
- https://docs.oracle.com/javase/7/docs/api/java/util/Collections.html
Happy Coding !!
Happy Learning !!