Java Java.util.LinkedList.offer(), offerFirst(), offerLast()方法

链接列表也有一个函数，用于 灵活地添加元素 ，并帮助在列表的前部和后部添加，这些函数字面意思是 “提供 “设施，名为offer()。有三种类型，在下面这篇文章中讨论。

offer(E e) : 这个方法将 指定的元素 添加到这个列表的 尾部 （最后一个元素）。

声明：
public boolean offer(E e)
参数 :
e:要添加的元素
返回值 :
该方法返回真

// Java code to demonstrate the working
// of offer(E e) in linked list
import java.util.*;
public class LinkedListoffer1 {
 
public static void main(String[] args)
    {
 
        // Declaring a LinkedList
        LinkedList list = new LinkedList();
 
        // adding elements
        list.add("Geeks");
        list.add(4);
        list.add("Geeks");
        list.add(8);
 
        // printing the list
        System.out.println("The initial Linked list is : " + list);
 
        // offering a new element
        // adds element at tail.
        list.offer("Astha");
 
        // printing the new list
        System.out.println("LinkedList after insertion using offer() : " + list);
    }
}

输出:

The initial Linked list is : [Geeks, 4, Geeks, 8]
LinkedList after insertion using offer() : [Geeks, 4, Geeks, 8, Astha]

offerFirst(E e) : 这个方法在这个列表的 前面 插入了 指定的元素。

**Declaration :**
   public boolean offerFirst(E e)
**Parameters :**
    **e :** the element to add
**Return Value :** 
    This method returns true

// Java code to demonstrate the working
// of offerFirst(E e) in linked list
import java.util.*;
public class LinkedListOfferFirst {
 
public static void main(String[] args)
    {
 
        // Declaring a LinkedList
        LinkedList list = new LinkedList();
 
        // adding elements
        list.add("Geeks");
        list.add(4);
        list.add("Geeks");
        list.add(8);
 
        // printing the list
        System.out.println("The initial Linked list is : " + list);
 
        // offering a new element
        // adds element at head.
        list.offerFirst("Astha");
 
        // printing the new list
        System.out.println("LinkedList after insertion using offerFirst() : " + list);
    }
}

输出:

The initial Linked list is : [Geeks, 4, Geeks, 8]
LinkedList after insertion using offerFirst() : [Astha, Geeks, 4, Geeks, 8]

offerLast(E e) : 这个方法在这个列表的 末尾 插入 指定的元素。

声明：
public boolean offerLast(E e)
参数 :
e:要添加的元素
返回值 :
该方法返回真

// Java code to demonstrate the working
// of offerLast(E e) in linked list
import java.util.*;
public class LinkedListOfferLast {
 
public static void main(String[] args)
    {
 
        // Declaring a LinkedList
        LinkedList list = new LinkedList();
 
        // adding elements
        list.add("Geeks");
        list.add(4);
        list.add("Geeks");
        list.add(8);
 
        // printing the list
        System.out.println("The initial Linked list is : " + list);
 
        // offering a new element
        // adds element at end.
        list.offerLast("Astha");
 
        // printing the new list
        System.out.println("LinkedList after insertion using offerLast() : " + list);
    }
}

输出:

The initial Linked list is : [Geeks, 4, Geeks, 8]
LinkedList after insertion using offerLast() : [Geeks, 4, Geeks, 8, Astha]

实际应用： 这些函数的 “灵活添加 “的质量可以在 队列中的优先级添加的 情况下进行，在这种情况下，比阈值大的元素必须在比它小的元素之前被处理。下面的一小段代码讨论了这个问题。

// Java code to demonstrate the application
// of offer() in linked list
import java.util.*;
public class LinkedListOfferLast {
 
public static void main(String[] args)
    {
 
        // Declaring LinkedLists
        LinkedList<Integer> list = new LinkedList<Integer>();
        LinkedList prioList = new LinkedList();
 
        // adding elements
        list.add(12);
        list.add(4);
        list.add(8);
        list.add(10);
        list.add(3);
        list.add(15);
 
        // declaring threshold
        int thres = 10;
 
        // printing the list
        System.out.println("The initial Linked list is : " + list);
 
        while (!list.isEmpty()) {
 
            int t = list.poll();
 
            // adding >=10 numbers at front rest at back
            if (t >= 10)
                prioList.offerFirst(t);
            else
                prioList.offerLast(t);
        }
 
        // The resultant list is
        System.out.println("The prioritized Linked list is : " + prioList);
    }
}

输出:

The initial Linked list is : [12, 4, 8, 10, 3, 15]
The prioritized Linked list is : [15, 10, 12, 4, 8, 3]