Java PriorityBlockingQueue add()方法

PriorityBlockingQueue 的 add(E e) 方法在这个PriorityBlockingQueue的尾部插入作为参数传递给该方法的元素。如果元素的添加成功，该方法返回true。否则就会返回false。

语法

public boolean add(E e)

参数： 该方法需要一个强制参数 e ，它是要插入PriorityBlockingQueue中的元素。

返回： 该方法返回一个 布尔 响应。如果元素的添加成功，它返回 true ，否则返回 false。

异常： 该方法会抛出以下异常。

• ClassCastException： 如果作为参数传递的元素不能与队列包含的元素进行比较，以保持优先队列的排序。
• NullPointerException： 如果作为参数传递的元素为空。

下面的程序说明了PriorityBlockingQueue的add()方法。

例1 :

// Java Program to Demonstrate add(E e) method
// of PriorityBlockingQueue.
 
import java.util.concurrent.PriorityBlockingQueue;
 
public class GFG {
 
    public static void main(String[] args)
    {
        // define capacity of PriorityBlockingQueue
        int capacity = 15;
 
        // create object of PriorityBlockingQueue
        PriorityBlockingQueue<Integer> PrioBlockingQueue
            = new PriorityBlockingQueue<Integer>(capacity);
 
        // add  numbers
        PrioBlockingQueue.add(526734);
        PrioBlockingQueue.add(84879456);
        PrioBlockingQueue.add(4586415);
 
        // print queue after add operation
        System.out.println("After Adding Some Numbers");
        System.out.println("PriorityBlockingQueue:"
                           + PrioBlockingQueue);
 
        // add more numbers
        PrioBlockingQueue.add(156116);
        PrioBlockingQueue.add(61651191);
 
        // print queue after add operation
        System.out.println("\nAfter adding Some More Numbers");
        System.out.println("PriorityBlockingQueue:"
                           + PrioBlockingQueue);
    }
}

输出

After Adding Some Numbers
PriorityBlockingQueue:[526734, 84879456, 4586415]

After adding Some More Numbers
PriorityBlockingQueue:[156116, 526734, 4586415, 84879456, 61651191]

例2： 演示add()方法抛出的NullPointerException。

// Java Program to Demonstrate Exception
// thrown by add(E e) method
// of PriorityBlockingQueue.
 
import java.util.concurrent.PriorityBlockingQueue;
 
public class GFG {
 
    public static void main(String[] args)
    {
        // define capacity of PriorityBlockingQueue
        int capacity = 15;
 
        // create object of PriorityBlockingQueue
        PriorityBlockingQueue<Integer> PrioBlockingQueue
            = new PriorityBlockingQueue<Integer>(capacity);
 
        // add numbers
        PrioBlockingQueue.add(526734);
        PrioBlockingQueue.add(84879456);
        PrioBlockingQueue.add(4586415);
        try {
            // try to add null to PrioBlockingQueue
            PrioBlockingQueue.add(null);
 
            // print PrioBlockingQueue after add operation
            System.out.println("PriorityBlockingQueue:"
                               + PrioBlockingQueue);
        }
        catch (Exception e) {
            System.out.println("Exception when adding null: "
                               + e);
        }
    }
}

输出

Exception when adding null: java.lang.NullPointerException

参考资料: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/PriorityBlockingQueue.html#add-E-