Java LinkedBlockingDeque的addFirst()方法

LinkedBlockingDeque 的 addFirst(E e) 方法会将传入的元素插入到Deque的前端（如果有空间）。如果LinkedBlockingDeque受到容量限制，没有插入的余地，它会返回一个异常 IllegalStateException 。

语法：

public void addFirst(E e)

参数： 此方法接受一个强制性参数 e 它是要插入LinkBlockingDeque前端的元素。

返回： 该方法不返回任何内容。

异常：

• IllegalStateException :如果由于容量限制，此时无法添加元素
• NullPointerException :如果指定的元素为null

以下程序演示了PriorityBlockingQueue的addFirst()方法：

程序1：

// Java Program Demonstrate addFirst()
// 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);

        // before removing print queue
        System.out.println("Linked Blocking Deque: " + LBD);
    }
}

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

程序2：

// Java Program Demonstrate addFirst()
// method of LinkedBlockingDeque
// when it is Full
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;

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

        // create object of LinkedBlockingDeque
        // size of list
        LinkedBlockingDeque<Integer> LBD
            = new LinkedBlockingDeque<Integer>(3);

        // Add numbers to front of LinkedBlockingDeque
        LBD.addFirst(7855642);
        LBD.addFirst(35658786);
        LBD.addFirst(5278367);

        // it is full
        LBD.addFirst(74381793);

        // before removing print queue
        System.out.println("Linked Blocking Deque: " + LBD);
    }
}

输出：

Exception in thread "main" java.lang.IllegalStateException: Deque full
    at java.util.concurrent.LinkedBlockingDeque.addFirst(LinkedBlockingDeque.java:326)
    at GFG.main(GFG.java:23)

程序3：

// Java程序演示LinkedBlockingDeque
// addFirst()方法插入空值时的情况
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {
  
        // 创建LinkedBlockingDeque对象
        LinkedBlockingDeque<Integer> LBD
            = new LinkedBlockingDeque<Integer>();
  
        // 在LinkedBlockingDeque前面添加数字
        LBD.addFirst(7855642);
        LBD.addFirst(35658786);
        LBD.addFirst(5278367);
  
        // NULL
        LBD.addFirst(null);
  
        // 在移除之前打印队列
        System.out.println("Linked Blocking Deque: " + LBD);
    }
}

输出:

Exception in thread "main" java.lang.NullPointerException
    at java.util.concurrent.LinkedBlockingDeque.offerFirst(LinkedBlockingDeque.java:342)
    at java.util.concurrent.LinkedBlockingDeque.addFirst(LinkedBlockingDeque.java:325)
    at GFG.main(GFG.java:22)

参考文献: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedBlockingDeque.html#add(E)