Java中的 BlockingQueue offer() 方法及示例

BlockingQueue 接口有两种类型的 offer() 方法：
注意： BlockingQueue的offer()方法继承自Java中的Queue类。

offer(E e, long timeout, TimeUnit 单位)

如果队列未满，BlockingQueue 的offer(E e, long timeout, TimeUnit unit)方法会将作为参数传递给方法的元素插入此BlockingQueue的尾部。如果 BlockingQueue 已满，它将等到指定时间才有可用空间。指定的等待时间和 TimeUnit 将作为参数提供给 offer() 方法。所以它会等到那个时候 BlockingQueue 删除一些元素，以便这个方法可以向 BlockingQueue 添加元素。
句法：

public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException

参数：此方法接受三个参数：

• e – 要插入 BlockingQueue 的元素。
• timeout - 直到提供方法将等待插入新元素的时间队列已满。
• unit – 超时参数的时间单位。

返回值：如果元素插入成功，该方法返回true 。否则，如果在空间可用之前经过指定的等待时间，则返回false 。
异常：此方法抛出以下异常：

• NullPointerException – 如果指定元素为空。
• InterruptedException – 如果在等待时被中断。

下面的程序说明了 BlockingQueue 类的 offer(E e, long timeout, TimeUnit unit) 方法：
方案一：

Java

// Java Program Demonstrate
// offer(Element e, long timeout, TimeUnit unit)
// method of BlockingQueue.
 
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
 
public class GFG {
 
    // Main method
    public static void main(String[] args)
        throws InterruptedException
    {
        // define capacity of BlockingQueue
        int capacityOfQueue = 4;
 
        // create object of BlockingQueue
        BlockingQueue
            BQ = new LinkedBlockingQueue(capacityOfQueue);
 
        // Add 5 elements to BlockingQueue having
        // Timeout in seconds with value 5 secs in
        // offer(Element e, long timeout, TimeUnit unit)
        System.out.println("adding 32673821 "
                           + BQ.offer(32673821,
                                      5,
                                      TimeUnit.SECONDS));
        System.out.println("adding 88527183: "
                           + BQ.offer(88527183,
                                      5,
                                      TimeUnit.SECONDS));
        System.out.println("adding 431278539: "
                           + BQ.offer(431278539,
                                      5,
                                      TimeUnit.SECONDS));
        System.out.println("adding 351278693: "
                           + BQ.offer(351278693,
                                      5,
                                      TimeUnit.SECONDS));
        System.out.println("adding 647264: "
                           + BQ.offer(647264,
                                      5,
                                      TimeUnit.SECONDS));
 
        // print the elements of queue
        System.out.println("list of numbers of queue:"
                           + BQ);
 
        // now queue is full check remaining capacity of queue
        System.out.println("Empty spaces of queue : "
                           + BQ.remainingCapacity());
 
        // try to add more Integer
        boolean response = BQ.offer(2893476,
                                    5,
                                    TimeUnit.SECONDS);
        System.out.println("Adding new Integer 2893476 is successful: "
                           + response);
    }
}

输出

adding 32673821 true
adding 88527183: true
adding 431278539: true
adding 351278693: true
adding 647264: false
list of numbers of queue:[32673821, 88527183, 431278539, 351278693]
Empty spaces of queue : 0
Adding new Integer 2893476 is successful: false

方案二：

Java

// Java Program Demonstrate
// offer(Element e, long timeout, TimeUnit unit)
// method of BlockingQueue.
 
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
 
public class GFG {
 
    public static void main(String[] args)
        throws InterruptedException
    {
        // define capacity of BlockingQueue
        int capacityOfQueue = 4;
 
        // create object of BlockingQueue
        BlockingQueue
            BQ = new LinkedBlockingQueue(capacityOfQueue);
 
        // Add elements to BlockingQueue having
        // Timeout in seconds with value 5 secs in
        // offer(Element e, long timeout, TimeUnit unit)
        System.out.println("Adding 283239 in Queue :"
                           + BQ.offer(283239,
                                      5,
                                      TimeUnit.SECONDS));
 
        // try to put null value in offer method
        try {
 
            System.out.println("Adding null in Queue: "
                               + BQ.offer(null,
                                          5,
                                          TimeUnit.SECONDS));
        }
        catch (Exception e) {
 
            // print error details
            System.out.println("Exception: " + e);
        }
 
        // print elements of queue
        System.out.println("Items in Queue are "
                           + BQ);
    }
}

输出：

Adding 283239 in Queue :true
Exception: java.lang.NullPointerException
Items in Queue are [283239]

报价(E e)

BlockingQueue 的offer(E e)方法在此BlockingQueue的尾部插入作为参数传递的元素 e，如果队列有空间，即队列未满。如果队列已满，则应用 offer() 方法无效，因为 BlockingQueue 将阻止要插入的元素。如果添加到 BlockingQueue 的操作成功，则 offer() 方法返回 true，如果队列已满，则返回 false。此方法优于 add() 方法，因为 add() 方法在队列已满时抛出错误，但 offer() 方法在这种情况下返回 false。
句法：

public boolean offer(E e)

参数：此方法采用强制参数e ，即要插入 LinkedBlockingQueue 的元素。
返回值：如果元素插入成功，此方法返回true 。否则返回false 。
异常：如果指定元素为空，该方法将抛出NullPointerException 。
下面的程序说明了 BlockingQueue 类的 offer() 方法
方案一：

Java

// Java Program Demonstrate
// offer(Element e)
// method of BlockingQueue.
 
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
 
public class GFG {
 
    // Main method
    public static void main(String[] args)
    {
        // define capacity of BlockingQueue
        int capacityOfQueue = 4;
 
        // create object of BlockingQueue
        BlockingQueue
            BQ = new LinkedBlockingQueue(capacityOfQueue);
 
        // Add element to BlockingQueue using offer
        BQ.offer("dean");
        BQ.offer("kevin");
        BQ.offer("sam");
        BQ.offer("jack");
 
        // print the elements of queue
        System.out.println("list of names of queue:");
        System.out.println(BQ);
    }
}

输出：

list of names of queue:
[dean, kevin, sam, jack]

方案二：

Java

// Java Program Demonstrate
// offer(Element e)
// method of BlockingQueue.
 
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
 
public class GFG {
 
    // Main method
    public static void main(String[] args)
    {
        // define capacity of BlockingQueue
        int capacityOfQueue = 4;
 
        // create object of BlockingQueue
        BlockingQueue
            BQ = new LinkedBlockingQueue(capacityOfQueue);
 
        // Add element to BlockingQueue using offer
        BQ.offer(34567);
        BQ.offer(45678);
        BQ.offer(98323);
        BQ.offer(93758);
 
        // print the elements of queue
        System.out.println("list of numbers of queue:");
        System.out.println(BQ);
 
        // now queue is full check remaining capacity of queue
        System.out.println("Empty spaces of queue : "
                           + BQ.remainingCapacity());
 
        // try to add extra Integer
        boolean response = BQ.offer(2893476);
 
        System.out.println("Adding new Integer 2893476 is successful: "
                           + response);
 
        response = BQ.offer(456751);
 
        System.out.println("Adding new Integer 456751 is successful: "
                           + response);
    }
}

输出

list of numbers of queue:
[34567, 45678, 98323, 93758]
Empty spaces of queue : 0
Adding new Integer 2893476 is successful: false
Adding new Integer 456751 is successful: false

程序 3：显示由 offer() 方法抛出的异常

Java

// Java Program Demonstrate offer(E e)
// method of LinkedBlockingQueue
 
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
 
public class GFG {
 
    public static void main(String[] args)
        throws InterruptedException
    {
        // define capacity of BlockingQueue
        int capacityOfQueue = 4;
 
        // create object of BlockingQueue
        BlockingQueue BQ
            = new LinkedBlockingQueue(capacityOfQueue);
 
        // Add element using offer() method
        BQ.offer("Karan");
 
        // try to put null value in offer method
        try {
            BQ.offer(null);
        }
        catch (Exception e) {
            // print error details
            System.out.println("Exception: " + e);
        }
 
        // print elements of queue
        System.out.println("Items in Queue are "
                           + BQ);
    }
}

输出：

Exception: java.lang.NullPointerException
Items in Queue are [Karan]

参考：

• https://docs.oracle.com/javase/7/docs/api/java Java)
• https://docs.oracle.com/javase/7/docs/api/java Java, %20long, %20java.util.concurrent.TimeUnit)