How to Append One List to Another List in Java

What is the method for appending one list to another in Java?

Appending a list to another list in Java can be achieved using several methods provided by the Java Collections Framework. The most common way is to use the `addAll()` method of the `List` interface, which is both efficient and straightforward.

import java.util.ArrayList;
import java.util.List;

public class ListAppendExample {
    public static void main(String[] args) {
        List<Integer> list1 = new ArrayList<>();
        list1.add(1);
        list1.add(2);
        list1.add(3);

        List<Integer> list2 = new ArrayList<>();
        list2.add(4);
        list2.add(5);

        // Appending list2 to list1
        list1.addAll(list2);

        // Displaying the combined list
        System.out.println("Combined List: " + list1);
    }
}

Causes

• Developers may not know the appropriate methods to concatenate lists.
• Performance considerations when dealing with large lists.

Solutions

• Use List's `addAll()` method for appending elements.
• Consider using `Stream.concat()` for a functional approach.
• Utilize a loop for custom appending logic.

Mistake: Using the `+=` operator for appending; not applicable in Java Lists.

Solution: Use `add()` or `addAll()` methods for adding elements.

Mistake: Not verifying if the list to be appended is `null`, leading to `NullPointerException`.

Solution: Always check if the list is `null` before performing operations.