How to copy a list to another list in Java?

A List of elements can be copied to another List in Java using multiple approaches. All methods create a shallow copy − the new list contains references to the same objects as the original.

Way 1: Constructor

Pass the source list to the ArrayList constructor −

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

Way 2: addAll()

Create an empty list and use addAll() to add all elements from the source −

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

Way 3: Collections.copy()

Use Collections.copy() to copy elements into an existing destination list. The destination list must already have enough elements (they get overwritten by index) −

Collections.copy(destList, sourceList);

Way 4: Streams (Java 8+)

Use the Stream API to collect elements into a new list −

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

Example

The following example demonstrates all four approaches ?

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<String> list = Arrays.asList("Zara", "Mahnaz", "Ayan");
        System.out.println("Source: " + list);

        // Way 1: Constructor
        List<String> copy1 = new ArrayList<>(list);
        System.out.println("Copy 1 (constructor): " + copy1);

        // Way 2: addAll()
        List<String> copy2 = new ArrayList<>();
        copy2.addAll(list);
        System.out.println("Copy 2 (addAll): " + copy2);

        // Way 3: Collections.copy()
        List<String> copy3 = Arrays.asList("Rob", "Julie", "John");
        Collections.copy(copy3, list);
        System.out.println("Copy 3 (Collections.copy): " + copy3);

        // Way 4: Streams
        List<String> copy4 = list.stream().collect(Collectors.toList());
        System.out.println("Copy 4 (stream): " + copy4);
    }
}

The output of the above code is ?

Source: [Zara, Mahnaz, Ayan]
Copy 1 (constructor): [Zara, Mahnaz, Ayan]
Copy 2 (addAll): [Zara, Mahnaz, Ayan]
Copy 3 (Collections.copy): [Zara, Mahnaz, Ayan]
Copy 4 (stream): [Zara, Mahnaz, Ayan]

Conclusion

The constructor approach is the simplest and most commonly used method for copying a list. All four methods create shallow copies, meaning changes to the objects inside the list will reflect in both the original and the copy.