Java.util.LinkedList.poll()，pollFirst()，pollLast()在Java中的示例

在Java中，LinkedList是一种常用的数据结构。它是一个双向链表，允许插入和删除操作。LinkedList类提供了一系列方法来对链表进行操作。其中，poll()，pollFirst()和pollLast()都是在链表中移除元素的方法。

Java.util.LinkedList.poll()

poll()方法从链表的头部移除一个元素，如果链表为空则返回null。

import java.util.LinkedList;

public class LinkedListExample {
    public static void main(String[] args) {
        LinkedList<String> linkedList = new LinkedList<>();
        linkedList.add("Apple");
        linkedList.add("Banana");
        linkedList.add("Orange");
        System.out.println("Original linkedList: " + linkedList);

        String removedElement = linkedList.poll();
        System.out.println("Element removed from the LinkedList: " + removedElement);
        System.out.println("LinkedList after removing an element using poll(): " + linkedList);
    }
}

输出：

Original linkedList: [Apple, Banana, Orange]
Element removed from the LinkedList: Apple
LinkedList after removing an element using poll(): [Banana, Orange]

Java.util.LinkedList.pollFirst()

pollFirst()方法从链表的头部移除一个元素，如果链表为空则返回null。

import java.util.LinkedList;

public class LinkedListExample {
    public static void main(String[] args) {
        LinkedList<String> linkedList = new LinkedList<>();
        linkedList.add("Apple");
        linkedList.add("Banana");
        linkedList.add("Orange");
        System.out.println("Original linkedList: " + linkedList);

        String removedElement = linkedList.pollFirst();
        System.out.println("Element removed from the LinkedList: " + removedElement);
        System.out.println("LinkedList after removing an element using pollFirst(): " + linkedList);
    }
}

输出：

Original linkedList: [Apple, Banana, Orange]
Element removed from the LinkedList: Apple
LinkedList after removing an element using pollFirst(): [Banana, Orange]

Java.util.LinkedList.pollLast()

pollLast()方法从链表的尾部移除一个元素，如果链表为空则返回null。

import java.util.LinkedList;

public class LinkedListExample {
    public static void main(String[] args) {
        LinkedList<String> linkedList = new LinkedList<>();
        linkedList.add("Apple");
        linkedList.add("Banana");
        linkedList.add("Orange");
        System.out.println("Original linkedList: " + linkedList);

        String removedElement = linkedList.pollLast();
        System.out.println("Element removed from the LinkedList: " + removedElement);
        System.out.println("LinkedList after removing an element using pollLast(): " + linkedList);
    }
}

输出：

Original linkedList: [Apple, Banana, Orange]
Element removed from the LinkedList: Orange
LinkedList after removing an element using pollLast(): [Apple, Banana]