Java BlockingDeque addFirst()方法及示例

BlockingDeque 的 addFirst(E e) 方法在有空间的情况下将参数中传递的元素插入到Deque的前面。如果BlockingDeque有容量限制，没有空间可以插入，它将返回一个IllegalStateException。

语法

public void addFirst(E e)

参数： 该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： 该方法不返回任何东西。

异常

• IllegalStateException ：如果由于容量的限制，此时不能添加该元素
• NullPointerException : 如果指定的元素是空的。

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

以下程序说明了BlockingQueue的addFirst()方法。

程序1 :

// 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<Integer> BD
            = new LinkedBlockingDeque<Integer>();
  
        // 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]

程序2 :

// 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<Integer> BD
            = new LinkedBlockingDeque<Integer>(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)

程序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<Integer> BD
            = new LinkedBlockingDeque<Integer>();
  
        // 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)

**参考资料: **https: //docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingDeque.html#addFirst(E)