Java BlockingDeque offerFirst()方法及示例

BlockingDeque 的 offerFirst(E e) 方法在Deque容器的前面插入参数中传递的元素。如果容器的容量超过了，那么它不会像add()和addFirst()函数那样返回一个异常。

语法

public boolean offerFirst(E e)

参数： 该方法接受一个强制性参数 e ，它是要在BlockingDeque前面插入的元素。

返回： 如果元素已经被插入，该方法返回 true ，否则返回 false 。

注意 ： BlockingDeque 的offerFirst()方法已经从Java的LinkedBlockingDeque类中继承。

下面的程序说明了LinkedBlockingDeque的offerFirst()方法。

程序1 :

// Java Program Demonstrate offerFirst()
// 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>(4);
 
        // Add numbers to end of BlockingDeque
        BD.offerFirst(7855642);
        BD.offerFirst(35658786);
        BD.offerFirst(5278367);
        BD.offerFirst(74381793);
 
        // Cannot be inserted
        BD.offerFirst(10);
 
        // cannot be inserted hence returns false
        if (!BD.offerFirst(10))
            System.out.println("The element 10 cannot be inserted"
                               + " as capacity is full");
 
        // before removing print queue
        System.out.println("Blocking Deque: " + BD);
    }
}

输出

The element 10 cannot be inserted as capacity is full
Blocking Deque: [74381793, 5278367, 35658786, 7855642]

程序2 :

// Java Program Demonstrate offerFirst()
// 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<String> BD
            = new LinkedBlockingDeque<String>(4);
 
        // Add numbers to end of BlockingDeque
        BD.offerFirst("abc");
        BD.offerFirst("gopu");
        BD.offerFirst("geeks");
        BD.offerFirst("richik");
 
        // Cannot be inserted
        BD.offerFirst("hii");
 
        // cannot be inserted hence returns false
        if (!BD.offerFirst("hii"))
            System.out.println("The element 'hii' cannot be"
                               + " inserted as capacity is full");
 
        // before removing print queue
        System.out.println("Blocking Deque: " + BD);
    }
}

输出

The element 'hii' cannot be inserted as capacity is full
Blocking Deque: [richik, geeks, gopu, abc]

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