在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一个 NoSuchElementException。

语法：

public E getLast()

参数： 此方法不接受任何参数。

返回值： 此方法返回此Deque容器的第一个元素或头部。

异常： 当deque为空时，函数仅抛出一个异常，即 NoSuchElementException

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

程序1：

// Java Program Demonstrate getFirst()
// method of LinkedBlockingDeque

import java.util.*;
import java.util.concurrent.LinkedBlockingDeque;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of LinkedBlockingDeque
        LinkedBlockingDeque<Integer> LBD
            = new LinkedBlockingDeque<Integer>();

        // 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());
    }
}

Linked Blocking Deque: [74381793, 5278367, 35658786, 7855642]
Linked Blocking Deque第一个元素：74381793

程序2：

// 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<Integer> LBD
            = new LinkedBlockingDeque<Integer>();
  
        // 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)

参考资料： https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedBlockingDeque.html#getFirst()