Java Collections copy() Method

The copy() method of Java Collections class copies all of the elements from one list into another list. In this method, the size of the destination list must be greater than or equal to the size of the source list.

Syntax

Following is the declaration of copy() method:

Parameter

Parameter	Description	Required/Optional
dest	It is a destination list in which elements are to be copied.	Required
src	It is the source list to be copied its elements into destination.	Required

Returns

The copy() method does not return anything.

Exceptions

The copy() method throws the following exceptions-

IndexOutOfBoundsException- It throws an exception if the destination list is too small to store the entire source List.

UnsupportedOperationException- It throws this type of exception if the destination list's list-iterator does not support the set operation.

Compatibility Version

Java 1.4 and above

Example 1

import java.util.*;
public class CollectionsCopyExample1 {
	public static void main(String[] args) {
		//Create lists for source and destination    
	      List<String> srclist = new ArrayList<String>(5);
	      List<String> destlist = new ArrayList<String>(10);
	      //Populate two source and destination lists
	      srclist.add("Java Tutorial");
	      srclist.add("is best on");
	      srclist.add("JavaTpoint");
	      destlist.add("JavaTpoint");
	      destlist.add("is older than");
	      destlist.add("SSSIT");
	      // copy into destination list
	      Collections.copy(destlist, srclist);            
	      System.out.println("Elements of source list: "+srclist);
	      System.out.println("Elements of destination list: "+destlist);
	      }
}

Test it Now

Output:

Elements of source list: [Java Tutorial, is best on, JavaTpoint]
Elements of destination list: [Java Tutorial, is best on, JavaTpoint]

Example 2

package myPackage;
import java.util.*;
public class CollectionsCopyExample2 {
	public static void main(String[] args) {
		//Create lists for source and destination    
		List<Integer> source = Arrays.asList(1,2,3,4);
    	      List<Integer> dest = Arrays.asList(5,6,7,8,9,10);
    	      Collections.copy(dest, source);
    	      //Print the List
    	      for(Integer i : dest) {
    		    System.out.print(i +" ");
	          }
	      }
}

Test it Now

Output:

1 2 3 4 9 10

Example 3

import java.util.*;
public class CollectionsCopyExample3 {
	public static void main(String[] args) {
		//Create lists for source and destination    
		List<Integer> source = Arrays.asList(1,2,3,4);
    	      List<Integer> dest = Arrays.asList(5,6,7);
    	      Collections.copy(dest, source);
    	      //Print the List	
    	      System.out.println(dest);
	      }
}	

Test it Now

Output:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Source does not fit in dest
	at java.base/java.util.Collections.copy(Collections.java:558)
	at myPackage.CollectionsCopyExample3.main(CollectionsCopyExample3.java:8)

Example 4

import java.util.*;
public class CollectionsCopyExample4 {
	@SuppressWarnings("unchecked")
	public static void main(String[] args) {
		//Create lists 		
		ArrayList source = new ArrayList();
		source.add(50);
		source.add(10);
		source.add(20);
	      System.out.println("Elements of Source List: " + source);   
		ArrayList dest = new ArrayList();
		dest.add("one");
		dest.add("two");
		dest.add("three");
		dest.add("four");
		dest.add("five");
	      System.out.println("Elements of Destination List: " + dest);	 
	      Collections.copy(dest, source);
	      System.out.println("Elements of Destination List after copying Source List: " + dest); 	
	      }
}

Test it Now

Output:

Elements of Source List: [50, 10, 20]
Elements of Destination List: [one, two, three, four, five]
Elements of Destination List after copying Source List: [50, 10, 20, four, five]

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