How Can I Efficiently Concatenate Lists in Java?

Concatenating Lists Efficiently in Java

One common task in Java programming is combining two lists into a single list. While the method described in the question is functional, it involves creating a new list and iterating over the existing lists to add their elements. Is there a more efficient way to achieve this?

The answer lies in using Java's Streams API. In Java 8 and later versions, the Stream.concat() method can merge two streams into a single stream. By leveraging this method, we can avoid creating a new list and perform the concatenation operation efficiently.

For example, in Java 8 and above, the code to concatenate two lists can be written as:

List<String> newList = Stream.concat(listOne.stream(), listTwo.stream())
                              .collect(Collectors.toList());

In Java 16 and above, the syntax can be simplified even further using the toList() method:

List<String> newList = Stream.concat(listOne.stream(), listTwo.stream()).toList();

These one-liners provide a concise and optimized solution to concatenating lists in Java. They adhere to the specified conditions by not modifying the original lists and using only the JDK, without external libraries.

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