Java LinkedBlockingDeque offerFirst()方法

LinkedBlockingDeque 的 offerFirst(E e) 方法在Deque容器的前面插入参数中传递的元素。如果容器的容量已经超过了，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参数 e ，它是要在LinkedBlockingDeque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 。

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

程序1 :

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

输出

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

示例2

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

输出

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

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