Interpretation of Java documentation: Analysis of the removeFirst() method function of the LinkedList class

The LinkedList class is one of the commonly used collection classes in Java. It is a doubly linked list structure. The LinkedList class provides many methods to operate linked lists, including addition, deletion and other operations. Among them, the removeFirst() method is an important method in the LinkedList class. This article will analyze the functions of this method and provide corresponding code examples to help readers better understand the use of this method.

1. removeFirst() method description

The removeFirst() method is used to delete the first element from the head of the linked list and return the value of the element. If the linked list is empty, this method will throw NoSuchElementException. The detailed definition of this method is as follows:

public E removeFirst() {
    if (size == 0)
        throw new NoSuchElementException();

    final Node<E> f = first;
    first = f.next;
    f.next = null;
    size--;
    return f.item;
}

2. Functional analysis of removeFirst() method

As can be seen from the above code, the specific implementation of the removeFirst() method is very simple . Below we will analyze the main functions of this method step by step:

(1) Determine whether the linked list is empty

At the beginning of the method, use the if statement to determine whether the size of the linked list is 0. If the linked list is empty, NoSuchElementException will be thrown, which is the first step of the removeFirst() method.

(2) Save the head node

As mentioned before, the main function of the removeFirst() method is to delete the head node of the linked list. Therefore, the first node must be saved before performing the linked list deletion operation.

(3) Modify the pointing of the head node

In order to delete the first element from the head of the linked list, the pointing of the head node must be modified. In this method, we assign the successor nodes of the head node to the head node. In this way, the head node points to the second node in the original linked list.

(4) Clear the reference of the deleted node

Since Java adopts an automatic garbage collection mechanism, after the node is deleted, there is still a part of the memory that has not been recycled by the automatic recycling mechanism. This part Memory occupies memory space. If it is not recycled for a long time, it will cause memory accumulation, and this phenomenon will make the memory usage of the program too high. Therefore, in order to avoid this situation from happening, the deleted node reference needs to be deleted from the memory to release the memory occupied by the node.

(5) Modify the number of elements in the linked list

After deleting an element, the number of elements in the linked list needs to be reduced by 1 accordingly.

(6) Return the value of the deleted element

Finally, this method returns the value of the deleted node. Since we have saved the head node in the second step, we can directly return the saved head node.

3. Code example of removeFirst() method

The following is a simple example of using the removeFirst() method, which contains the following main steps:

(1) Create a LinkedList object and add some elements;

(2) Use the removeFirst() method to delete the first element of the linked list;

(3) Output the deleted elements Elements of the linked list.

import java.util.LinkedList;

public class RemoveFirstTest {

    public static void main(String[] args) {
        LinkedList<String> list = new LinkedList<>();

        list.add("A");
        list.add("B");
        list.add("C");

        System.out.println("Before remove first: " + list);

        String first = list.removeFirst();

        System.out.println("Deleted element: " + first);
        System.out.println("After remove first: " + list);
    }
}

Run the above code, the output result is as follows:

Before remove first: [A, B, C]
Deleted element: A
After remove first: [B, C]

As can be seen from the output result, this method successfully deletes the first element of the linked list and correctly returns the value of the element .

4. Conclusion

The LinkedList class is one of the commonly used collection classes in Java, and the removeFirst() method is one of the important methods. This article analyzes the internal functions of this method and provides corresponding code examples to help readers better understand the use of this method. Hope this article can provide you with some help.

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