Java 中的 LinkedBlockingDeque offerFirst() 方法

LinkedBlockingDeque 中的 offerFirst(E e) 方法将传递给参数的元素插入到 Deque 容器的前面。如果容器的容量已满，则不会像 add() 和 addFirst() 函数一样返回异常。

语法：

public boolean offerFirst(E e)

参数： 该方法接受一个必填参数 e ，即要插入到 LinkedBlockingDeque 前面的元素。

返回值： 如果已插入元素，则该方法返回 true ，否则返回 false。

下面的程序演示了 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]

程序 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)