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Java Collections copy() Method with Example

Collections Class copy() method: Here, we are going to learn about the copy() method of Collections Class with its syntax and example.
Submitted by Preeti Jain, on February 03, 2020

Collections Class copy() method

• copy() method is available in java.util package.
• copy() method is used to copy all the elements from List the src_list (source list) and place all the copied elements into List dst_list (destination list).
• copy() method is a static method, so it is accessible with the class name and if we try to access the method with the class object then we will not get an error.
• copy() method may throw an exception at the time of copying elements from one list to another.
  • IndexOutOfBoundsException: This exception may throw when the given parameter dst_list size is lesser than the src_list.
  • UnsupportedOperationException: This exception may throw when the given parameter dst_list un-support set operation.

Syntax:

    public static void copy(List dst_list, List src_list);

Parameter(s):

• List dst_list – represents the destination list.
• List src_list – represents the source list.

Return value:

The return type of this method is void, it returns nothing.

Example:

// Java program is to demonstrate the example of
// void copy() method of Collections 

import java.util.*;

public class Copy {
    public static void main(String args[]) {
        // Instantiate two LinkedList object
        List < Integer > src_l = new LinkedList < Integer > ();
        List < Integer > dest_l = new LinkedList < Integer > ();

        // By using add() method is to add
        // few elements in src_l
        src_l.add(10);
        src_l.add(20);
        src_l.add(30);
        src_l.add(40);

        // By using add() method is to add
        // few elements in dest_l
        dest_l.add(60);
        dest_l.add(70);
        dest_l.add(80);
        dest_l.add(90);

        // Display LinkedList
        System.out.println("src_l: " + src_l);
        System.out.println("dest_l: " + dest_l);

        // By using copy() method is to
        // copy the elements of src_l into a dest_l
        Collections.copy(dest_l, src_l);

        System.out.println();

        // Display Copied LinkedList
        System.out.println("Collections.copy(dest_l, src_l): " + dest_l);
    }
}

Output

src_l: [10, 20, 30, 40]
dest_l: [60, 70, 80, 90]

Collections.copy(dest_l, src_l): [10, 20, 30, 40]