Introduction:

In Java, the Deque interface provides a double-ended queue, which allows elements to be added or removed from both ends. However, there may be situations where you need to convert a Deque to a List, which provides more flexibility and functionality. This blog post will explore different methods for converting a Deque to a List in Java, along with their respective advantages and disadvantages. We will provide code examples, outputs, and detailed explanations for each method, enabling you to make an informed choice based on your specific requirements.

Method 1: Using ArrayList's constructor

One of the simplest ways to convert a Deque to a List is by using the constructor of the ArrayList class. Here's the code:

Deque<String> deque = new LinkedList<>();
deque.add("Apple");
deque.add("Banana");
deque.add("Orange");

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

In this method, we create an empty ArrayList and pass the Deque as an argument to its constructor. The elements from the Deque are copied to the ArrayList, preserving their order. The resulting ArrayList can now be used as a List.

Output:

The resulting ArrayList, list, will contain the elements in the same order as the original Deque: ["Apple", "Banana", "Orange"].

Method 2: Using the addAll() method

Another approach is to use the addAll() method of the ArrayList class. Here's the code:

Deque<String> deque = new LinkedList<>();
deque.add("Apple");
deque.add("Banana");
deque.add("Orange");

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

In this method, we create an empty ArrayList and use the addAll() method to add all the elements from the Deque. The order of the elements is preserved, and the resulting ArrayList can be treated as a List.

Output:

The resulting ArrayList, list, will also contain the elements in the same order as the original Deque: ["Apple", "Banana", "Orange"].

Method 3: Using a loop

If you prefer a more manual approach, you can iterate over the elements of the Deque and add them to an ArrayList one by one. Here's the code:

Deque<String> deque = new LinkedList<>();
deque.add("Apple");
deque.add("Banana");
deque.add("Orange");

List<String> list = new ArrayList<>();
for (String element : deque) {
    list.add(element);
}

This method involves iterating over the elements of the Deque using an enhanced for loop and adding each element to the ArrayList. This approach provides more control and flexibility if you need to perform any additional operations during the conversion process.

Output:

The resulting ArrayList, list, will have the same elements in the same order as the original Deque: ["Apple", "Banana", "Orange"].

Conclusion:

Converting a Deque to a List in Java can be accomplished using several different strategies. In this blog post, we explored three effective methods: using the ArrayList constructor, utilizing the addAll() method, and using a loop to manually add elements. Each method has its advantages, depending on the specific requirements of your application. The first method, using the ArrayList constructor, is the most straightforward and concise. It provides a convenient way to create an ArrayList directly from a Deque, with the elements maintaining their original order. The second method, using the addAll() method, allows you to add all elements from a Deque to an existing ArrayList. This method is useful when you already have an ArrayList instance or when you want to concatenate multiple Deques into a single List. The third method, using a loop, provides more flexibility if you need to perform additional operations during the conversion process. However, it requires more manual coding and may be less efficient for large Deques.