Java PriorityBlockingQueue add()用法及代碼示例

PriorityBlockingQueue的add(E e)方法將作為參數傳遞的元素插入到此PriorityBlockingQueue尾部的方法中。如果成功添加元素，則此方法返回true。否則返回false。

用法:

public boolean add(E e)

參數：此方法采用強製參數e，該參數是要插入PriorityBlockingQueue的元素。

返回值：此方法返回布爾響應。如果成功添加元素，則返回true，否則返回false。

異常：此方法引發以下異常：

ClassCastException：如果不能將作為參數傳遞的元素與隊列包含的元素進行比較以保持優先級隊列的順序。
NullPointerException ：如果作為參數傳遞的元素為null。

以下示例程序旨在說明PriorityBlockingQueue的add()方法：

示例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); 
    } 
}

輸出：

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

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

示例2:演示由add()方法引發的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); 
        } 
    } 
}

輸出：

Exception when adding null: java.lang.NullPointerException

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

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