Java中的 LinkedBlockingDeque getFirst() 方法

LinkedBlockingDeque的getFirst()方法返回 Deque 容器中最前面的元素。如果 LinkedBlockingDeque 为空，则在函数调用时返回NoSuchElementException 。

句法：

public E getLast()

参数：此方法不接受任何参数。

返回：此方法返回此 Deque 容器的第一个元素或头部。

异常：当双端队列为空时，该函数仅抛出一个异常，即NoSuchElementException

下面的程序说明了 LinkedBlockingDeque 的 getFirst() 方法：

方案一：

// Java Program Demonstrate getFirst()
// method of LinkedBlockingDeque
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {
  
        // create object of LinkedBlockingDeque
        LinkedBlockingDeque LBD
            = new LinkedBlockingDeque();
  
        // Add numbers to front of LinkedBlockingDeque
        LBD.addFirst(7855642);
        LBD.addFirst(35658786);
        LBD.addFirst(5278367);
        LBD.addFirst(74381793);
  
        // before removing print queue
        System.out.println("Linked Blocking Deque: " + LBD);
  
        // prints the first element
        System.out.println("Linked Blocking Deque first element: " + 
                                                    LBD.getFirst());
    }
}

输出：

Linked Blocking Deque: [74381793, 5278367, 35658786, 7855642]
Linked Blocking Deque first element: 74381793

方案二：

// Java Program Demonstrate getFirst()
// method of LinkedBlockingDeque
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {
  
        // create object of LinkedBlockingDeque
        LinkedBlockingDeque LBD
            = new LinkedBlockingDeque();
  
        // Add numbers to front of LinkedBlockingDeque
        LBD.addFirst(7855642);
        LBD.addFirst(35658786);
        LBD.addFirst(5278367);
        LBD.addFirst(74381793)
  
            LBD.clear();
  
        // Since the container is empty it will throw exception
        System.out.println("Linked Blocking Deque first element: " + 
                                                    LBD.getFirst());
    }
}

输出：

Exception in thread "main" java.util.NoSuchElementException
    at java.util.concurrent.LinkedBlockingDeque.getFirst(LinkedBlockingDeque.java:553)
    at GFG.main(GFG.java:28)

参考： https: Java/util/concurrent/LinkedBlockingDeque.html#getFirst()