Java中的 BlockingDeque addFirst() 方法及示例

BlockingDeque的addFirst(E e)方法，如果有空格，则将参数中传入的元素插入到 Deque 的前面。如果 BlockingDeque 容量受限且没有空间可插入，则返回IllegalStateException 。

句法：

public void addFirst(E e)

参数：此方法接受一个强制参数e ，它是要插入到 BlockingDeque 前面的元素。

返回：此方法不返回任何内容。

例外：

• IllegalStateException : 如果此时由于容量限制无法添加元素
• NullPointerException : 如果指定元素为 null

注意： BlockingDeque的 addFirst() 方法继承自Java中的 LinkedBlockingDeque 类。

下面的程序说明了 BlockingQueue 的 addFirst() 方法：

方案一：

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

输出：

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

方案二：

// Java Program Demonstrate addFirst()
// method of BlockingDeque
// when it is Full
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {
  
        // create object of BlockingDeque
        // size of list
        BlockingDeque BD
            = new LinkedBlockingDeque(3);
  
        // Add numbers to front of BlockingDeque
        BD.addFirst(7855642);
        BD.addFirst(35658786);
        BD.addFirst(5278367);
  
        // it is full
        BD.addFirst(74381793);
  
        // before removing print Deque
        System.out.println("Blocking Deque: " + BD);
    }
}

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:24)

方案 3：

// Java Program Demonstrate addFirst()
// method of BlockingDeque
// when nill is inserted
  
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {
  
        // create object of BlockingDeque
        BlockingDeque BD
            = new LinkedBlockingDeque();
  
        // Add numbers to front of BlockingDeque
        BD.addFirst(7855642);
        BD.addFirst(35658786);
        BD.addFirst(5278367);
  
        // NULL
        BD.addFirst(null);
  
        // before removing print Deque
        System.out.println("Blocking Deque: " + BD);
    }
}

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:24)

参考： https: Java/util/concurrent/BlockingDeque.html#addFirst(E)