How to use Deque function in Java for deque operations

Double-ended queue (Deque) is a relatively complex data structure with queue and stack characteristics. It supports all operations of queues and stacks, and can add or delete elements at the head and tail of the queue. In Java, Deque is an interface, which has two implementation classes: ArrayDeque and LinkedList.

This article will introduce how to use the Deque function in Java to perform double-ended queue operations, including creating Deque, adding elements, removing elements, head and tail operations, etc.

1. Create Deque

To create a Deque object in Java, you can use the ArrayDeque or LinkedList implementation class. If the number of elements is known and performance requirements are high, it is better to use ArrayDeque; if the number of elements is uncertain, or elements need to be frequently inserted or deleted in the middle, it is better to use LinkedList.

The following is the code to create a Deque object named deque:

Deque<String> deque = new ArrayDeque<String>(); // 使用ArrayDeque实现类创建
Deque<Integer> deque = new LinkedList<Integer>(); // 使用LinkedList实现类创建

2. Add elements

Adding elements is one of the basic operations of a double-ended queue. In Deque, elements can be added to the head or tail of the queue. Use the addFirst() and addLast() methods respectively to add.

Use addFirst() to add elements:

deque.addFirst("element");

Use addLast() to add elements:

deque.addLast("element");

If the double-ended queue is full during the addition process, addFirst() will throw An IllegalStateException occurs.

3. Remove elements

Removing elements is also one of the basic operations of a double-ended queue. In Deque, you can also remove elements from the head or tail of the queue. Use the removeFirst() and removeLast() methods respectively to remove.

Use removeFirst() to remove elements:

String element = deque.removeFirst();

Use removeLast() to remove elements:

String element = deque.removeLast();

If the queue is empty, calling the above method will throw a NoSuchElementException exception.

4. Determine elements

Sometimes we need to determine whether the Deque contains a certain element or what the first and last elements are. At this time, you can use element(), peek() and other methods.

Use element() to get the first element of the team:

String firstElement = deque.element(); // 队首元素

Use peek() to get the first element of the team:

String firstElement = deque.peek(); // 队首元素

If the queue is empty, calling the above method will throw NoSuchElementException abnormal.

Use peekFirst() to get the first element of the team:

String firstElement = deque.peekFirst(); // 队首元素

Use peekLast() to get the last element of the team:

String lastElement = deque.peekLast(); // 队尾元素

5. Traversing elements

During traversal For elements in Deque, you can use Iterator, foreach or lambda expressions to perform traversal operations.

Traverse using Iterator:

Iterator<String> iterator = deque.iterator(); // 获取Iterator对象
while (iterator.hasNext()) { // 依次输出元素
    System.out.println(iterator.next());
}

Traverse using foreach:

for (String element : deque) { // 依次输出元素
    System.out.println(element);
}

Traverse using lambda expression:

deque.forEach(element -> System.out.println(element)); // 依次输出元素

Summary

Deque is The interface of double-ended queue in Java provides all operations of queue and stack. You can add or delete elements at the head of the queue and add or delete elements at the tail of the queue. In Java, Deque has two implementation classes: ArrayDeque and LinkedList, which are used in different scenarios.

This article introduces how to use the Deque function in Java to perform double-ended queue operations, including creating Deque, adding elements, removing elements, head and tail operations, and traversing elements. Dedicated to providing help to Java beginners, more articles are on this site!

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