Java Deque element()方法

Deque接口 的 element() 方法返回容器中最前面的元素。它不会删除容器中的元素。这个方法返回Deque的头部。当Deque为空时，该方法会抛出一个异常。

语法：

E element()

参数： 该方法不接受任何参数。

返回： 该方法返回容器前端或Deque头部的元素。

异常： 当Deque为空时，该函数会抛出NoSuchElementException。

以下程序说明了Deque的element()方法：

程序1： 借助 LinkedList

// Java Program Demonstrate element()// method of Dequeimport java.util.*; public class GFG {    public static void main(String[] args)        throws IllegalStateException    {         // create object of Deque        Deque<Integer> DQ            = new LinkedList<Integer>();         // Add numbers to end of Deque        DQ.add(7855642);        DQ.add(35658786);        DQ.add(5278367);        DQ.add(74381793);         // print Deque        System.out.println("Deque: " + DQ);         // print head        System.out.println("Deque's head: " + DQ.element());    }}

输出

Deque: [7855642, 35658786, 5278367, 74381793]Deque's head: 7855642

程序2： 在 ArrayDeque 的帮助下 。

// Java Program Demonstrate element()// method of Dequeimport java.util.*; public class GFG {    public static void main(String[] args)        throws IllegalStateException    {         // create object of Deque        Deque<Integer> DQ            = new ArrayDeque<Integer>();         // Add numbers to end of Deque        DQ.add(7855642);        DQ.add(35658786);        DQ.add(5278367);        DQ.add(74381793);         // print Deque        System.out.println("Deque: " + DQ);         // print head        System.out.println("Deque's head: " + DQ.element());    }}

输出

Deque: [7855642, 35658786, 5278367, 74381793]Deque's head: 7855642

程序3： 在 ConcurrentLinkedDeque 的帮助下 。

// Java Program Demonstrate element()// method of Dequeimport java.util.*;import java.util.concurrent.ConcurrentLinkedDeque; public class GFG {    public static void main(String[] args)        throws IllegalStateException    {         // create object of Deque        Deque<Integer> DQ            = new ConcurrentLinkedDeque<Integer>();         // Add numbers to end of Deque        DQ.add(7855642);        DQ.add(35658786);        DQ.add(5278367);        DQ.add(74381793);         // print Deque        System.out.println("Deque: " + DQ);         // print head        System.out.println("Deque's head: " + DQ.element());    }}

输出

Deque: [7855642, 35658786, 5278367, 74381793]Deque's head: 7855642

程序4： 在 LinkedBlockingDeque 的帮助下 。

// Java Program Demonstrate element()// method of Dequeimport java.util.*;import java.util.concurrent.LinkedBlockingDeque; public class GFG {    public static void main(String[] args)        throws IllegalStateException    {         // create object of Deque        Deque<Integer> DQ            = new LinkedBlockingDeque<Integer>();         // Add numbers to end of Deque        DQ.add(7855642);        DQ.add(35658786);        DQ.add(5278367);        DQ.add(74381793);         // print Deque        System.out.println("Deque: " + DQ);         // print head        System.out.println("Deque's head: " + DQ.element());    }}

输出

Deque: [7855642, 35658786, 5278367, 74381793]Deque's head: 7855642

程序2

// Java Program Demonstrate element()// method of Dequeimport java.util.*; public class GFG {    public static void main(String[] args)        throws IllegalStateException    {         // create object of Deque        Deque<Integer> DQ            = new LinkedList<Integer>();         // Add numbers to end of Deque        DQ.add(7855642);        DQ.add(35658786);        DQ.add(5278367);        DQ.add(74381793);         // print Deque        System.out.println("Deque: " + DQ);         // print head        System.out.println("Deque's head: " + DQ.element());         DQ.clear();         // Deque is empty now hence exception        System.out.println("Deque's head: " + DQ.element());    }}

输出

Exception in thread "main" java.util.NoSuchElementException    at java.util.LinkedList.getFirst(LinkedList.java:244)    at java.util.LinkedList.element(LinkedList.java:663)    at GFG.main(GFG.java:29)

参考资料: https://docs.oracle.com/javase/8/docs/api/java/util/Deque.html#element-