Java Collections nCopies() Method

The nCopies() method of Java Collections class is used to get an immutable list consisting of n copies of the specified object.

Syntax

Following is the declaration of nCopies() method:

Parameter

Parameter	Description	Required/Optional
n	It is the number of elements in the returned list.	Required
o	It is the element to appear repetedly in the returned list.	Required

Returns

The nCopies() method returns an immutable list consisting of n copies of the specified object.

Exceptions

IllegalArgumentException- It throws this exception if the number of elements is less then zero i.e. n < 0.

Compatibility Version

Java 1.4 and above

Example 1

import java.util.*;
public class CollectionsNCopiesExample1 {
	public static void main(String[] args) {		
		List<String> list = Collections.nCopies(3, "JavaTpoint");
            System.out.println("Output: "+list);	      
	      }
}

Test it Now

Output:

Output: [JavaTpoint, JavaTpoint, JavaTpoint]

Example 2

import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
public class CollectionsNCopiesExample2 {
	public static void main(String[] args) {		
		AtomicInteger ai = new AtomicInteger();
            List<AtomicInteger> list = Collections.nCopies(3, ai);
            System.out.println("Output of Atomic Integer are:");
            System.out.println(list);
            ai.incrementAndGet();
            System.out.println(list);     
	      }
}

Test it Now

Output:

Output of Atomic Integer are:
[0, 0, 0]
[1, 1, 1]

Example 3

import java.util.*;
public class CollectionsNCopiesExample3 {
	public static void main(String[] args) {		
		List<String> list = Collections.nCopies(5,"SSSIT.COM");	
		System.out.println("List elements: ");
		Iterator<String> it = list.iterator();
		while(it.hasNext())
		System.out.println(it.next());  
	      }
}

Test it Now

Output:

List elements: 
SSSIT.COM
SSSIT.COM
SSSIT.COM
SSSIT.COM
SSSIT.COM

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Java Collections nCopies() Method

Syntax

Parameter

Returns

Exceptions

Compatibility Version

Example 1

Example 2

Example 3