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Collections.nCopies() in Java
  • Difficulty Level : Hard
  • Last Updated : 28 Feb, 2018

The role of Collections.nCopies() is to return an immutable list which contains n copies of given object. This function helps if we want to create a list with n copies of given object. The newly allocated data object is tiny i.e, it contains a single reference to the data object.

Syntax :

public static <T> List<T> nCopies(int number, T object)

where, number is the number of copies
of object and object represents the 
element which will appear number times
in the returned list. T represents generic type. 

Exception : The function throws IllegalArgumentException if value of number is less than 0.

Example :

Java




// Java code to show implementation
// of Collections.nCopies()
import java.util.*;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // creating a list where first argument
        // represents the number of copies and
        // the second argument represents the
        // element to be copied for 'number' times
        // This will create 4 copies of the objects.
        List list = Collections.nCopies(4, "GeeksforGeeks");
  
        // Displaying the list returned
        System.out.println("The list returned is :");
        Iterator itr = list.iterator();
        while (itr.hasNext()) {
            System.out.print(itr.next() + " ");
        }
        System.out.println("\n");
  
        List list1 = Collections.nCopies(3, "GeeksQuiz");
      
        // Displaying the list returned
        System.out.println("The list returned is :");
        Iterator itr1 = list1.iterator();  
        while (itr1.hasNext()) {
            System.out.print(itr1.next() + " ");
        }
        System.out.print("\n");
    }
}



Output :

The list returned is :
GeeksforGeeks GeeksforGeeks GeeksforGeeks GeeksforGeeks 

The list returned is :
GeeksQuiz GeeksQuiz GeeksQuiz  

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