How to copy a list in Java?

There are several ways to copy a list of elements into another list.

Way #1

Create a list by passing another list as a constructor parameter.

List<String> copyOflist = new ArrayList<>(list);

Create a list and add all elements of the source list to it using the addAll method.

Method #2

List<String> copyOfList = new ArrayList<>();
copyOfList.addAll(list);

Method #3

Use the Collections.copy method to copy the contents of the source list to the target list. If an index exists, existing elements will be overwritten.

Collections.copy(copyOfList, list);

Way #4

Use a stream to create a copy of the list.

List<String> copyOfList = list.stream().collect(Collectors.toList());

Example

The following is an example to explain using various methods to create a copy of a List object.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;

public class CollectionsDemo {
   public static void main(String[] args) {
      List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
      System.out.println("Source: " + list);
      List<Integer> copyOfList1 = new ArrayList<>(list);
      System.out.println("Copy 1: " + copyOfList1);
      List<Integer> copyOfList2 = new ArrayList<>();
      copyOfList2.addAll(list);
      System.out.println("Copy 2: " + copyOfList2);
      List<Integer> copyOfList3 = Arrays.asList(6, 7, 8, 9, 0 );
      Collections.copy(copyOfList3, list);
      System.out.println("Copy 3: " + copyOfList3);
      List<Integer> copyOfList4 = list.stream().collect(Collectors.toList());
      System.out.println("Copy 4: " + copyOfList4);
   }
}

Output

This will produce the following results −

Source: [1, 2, 3, 4, 5]
Copy 1: [1, 2, 3, 4, 5]
Copy 2: [1, 2, 3, 4, 5]
Copy 3: [1, 2, 3, 4, 5]
Copy 4: [1, 2, 3, 4, 5]

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