Java.util.LinkedList.get()、getFirst()、getLast() 在Java中

允许获取特定索引处的元素的常规方法是 get()。尽管在 LinkedList 中，如果没有完全遍历，它永远不可能实现这一点，但这种方法允许相同。存在三个变体，所有这些变体都在本文中进行了讨论，同时也带有例外。
1. get(int index) ：此方法返回此列表中指定位置的元素。

Declaration : 
    public E get(int index)
Parameters : 
    index :  index of the element to return
Return Value : 
   This method returns the element at the specified position in this list
Exception
     IndexOutOfBoundsException : if the index is out of range

// Java code to demonstrate the working
// of get(int index) in linked list
import java.util.*;
public class LinkedListget1 {
public static void main(String[] args)
    {
        // declaring a LinkedList
        LinkedList list = new LinkedList();
  
        // adding elements using add()
        list.add("Geeks");
        list.add("4");
        list.add("Geeks");
        list.add("8");
  
        // printing the whole list
        System.out.println("The elements in List are : " + list);
  
        // using get() to print element at index 3
        // prints 8
        System.out.println("Element at index 3 is : " + list.get(3));
    }
}

输出 ：

The elements in List are : [Geeks, 4, Geeks, 8]
Element at index 3 is : 8

2. getFirst() ：此方法返回此列表中的第一个元素。

Declaration : 
    public E getFirst()
Return Value : 
    This method returns the first element in this list
Exceptions : 
     NoSuchElementException : if this list is empty

// Java code to demonstrate the working
// of getFirst() in linked list
import java.util.*;
public class LinkedListget2 {
public static void main(String[] args)
    {
        // declaring a LinkedList
        LinkedList list = new LinkedList();
  
        // adding elements using add()
        list.add("Geeks");
        list.add("4");
        list.add("Geeks");
        list.add("8");
  
        // printing the whole list
        System.out.println("The elements in List are : " + list);
  
        // using get() to print element at first index
        // prints "Geeks"
        System.out.println("Element at 1st index is : " + list.getFirst());
    }
}

输出 ：

The elements in List are : [Geeks, 4, Geeks, 8]
Element at 1st index is : Geeks

3. getLast() ：此方法返回此列表中的最后一个元素。

Declaration : 
    public E getLast()
Return Value : 
   This method returns the last element in this list
Exceptions : 
   NoSuchElementException : if this list is empty

// Java code to demonstrate the working
// of getLast() in linked list
import java.util.*;
public class LinkedListget3 {
public static void main(String[] args)
    {
        // declaring a LinkedList
        LinkedList list = new LinkedList();
  
        // adding elements using add()
        list.add("Geeks");
        list.add("4");
        list.add("Geeks");
        list.add("8");
  
        // printing the whole list
        System.out.println("The elements in List are : " + list);
  
        // using get() to print element at last index
        // prints "8"
        System.out.println("Element at last index is : " + list.getLast());
    }
}

输出：

The elements in List are : [Geeks, 4, Geeks, 8]
Element at last index is : 8

例外

1. IndexOutOfBoundException

// Java code to demonstrate the Exceptions
// of get()
import java.util.*;
public class LinkedListExcep1 {
public static void main(String[] args)
    {
        // declaring a LinkedList
        LinkedList list = new LinkedList();
  
        // adding elements using add()
        list.add("Geeks");
        list.add("4");
        list.add("Geeks");
        list.add("8");
  
        // Trying to get element at index 7
        // throws exception
        System.out.println("The element at index 7 is : " + list.get(7));
    }
}

输出 ：

No Output

运行时错误：

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 7, Size: 4
    at java.util.LinkedList.checkElementIndex(LinkedList.java:555)
    at java.util.LinkedList.get(LinkedList.java:476)
    at LinkedListExcep1.main(LinkedListExcep1.java:22)

2. NoSuchElementException

// Java code to demonstrate the Exceptions
// of getFirst()
import java.util.*;
public class LinkedListExcep2 {
public static void main(String[] args)
    {
        // declaring a LinkedList
        LinkedList list = new LinkedList();
  
        // Trying to get first element at index 7
        // throws exception
        System.out.println("The first element of list is : " + list.getFirst());
    }
}

输出 ：

No Output

运行时错误：

Exception in thread "main" java.util.NoSuchElementException
    at java.util.LinkedList.getFirst(LinkedList.java:244)
    at LinkedListExcep2.main(LinkedListExcep2.java:15)