Java ArrayBlockingQueue toArray()用法及代碼示例

1. toArray()方法ArrayBlockingQueue類：
   ArrayBlockingQueue類的toArray()方法用於按適當順序創建一個數組，該數組包含與此ArrayBlockingQueue相同的元素。本質上，它將所有元素從ArrayBlockingQueue複製到新數組。此方法充當數組和集合之間的橋梁。

   用法:

   public Object[] toArray()

   返回值：該方法返回一個包含此隊列中所有元素的數組。

   
   

   下麵的程序說明ArrayBlockingQueue類的toArray()方法：
   示例1:

   // Program Demonstrate how to apply toArray() method 
   // of ArrayBlockingQueue Class. 
     
   import java.util.concurrent.ArrayBlockingQueue; 
     
   public class GFG { 
     
       public static void main(String[] args) 
       { 
           // Define capacity of ArrayBlockingQueue 
           int capacity = 5; 
     
           // Create object of ArrayBlockingQueue 
           ArrayBlockingQueue<Integer> queue = new 
                        ArrayBlockingQueue<Integer>(capacity); 
     
           // Add 5 elements to ArrayBlockingQueue 
           queue.offer(423); 
           queue.offer(422); 
           queue.offer(421); 
           queue.offer(420); 
           queue.offer(424); 
     
           // Create a array by calling toArray() method 
           Object[] array = queue.toArray(); 
     
           // Print queue 
           System.out.println("Queue is " + queue); 
     
           // Print elements of array 
           System.out.println("The array created by toArray() is:"); 
           for (Object i : array) { 
               System.out.println(i); 
           } 
       } 
   }

   輸出：

   Queue is [423, 422, 421, 420, 424]
   The array created by toArray() is:
   423
   422
   421
   420
   424
   

   示例2:

   // Program Demonstrate how to apply toArray() method 
   // of ArrayBlockingQueue Class. 
     
   import java.util.concurrent.ArrayBlockingQueue; 
     
   public class GFG { 
     
       public static void main(String[] args) 
       { 
           // Define capacity of ArrayBlockingQueue 
           int capacity = 5; 
     
           // Create object of ArrayBlockingQueue 
           ArrayBlockingQueue<String> queue = new 
                         ArrayBlockingQueue<String>(capacity); 
     
           // Add 5 elements to ArrayBlockingQueue 
           queue.offer("User"); 
           queue.offer("Employee"); 
           queue.offer("Manager"); 
           queue.offer("Analyst"); 
           queue.offer("HR"); 
     
           // Create a array by calling toArray() method 
           Object[] array = queue.toArray(); 
     
           // Print queue 
           System.out.println("Queue is " + queue); 
     
           // Print elements of array 
           System.out.println("The array created by toArray() is:"); 
           for (Object i : array) { 
               System.out.println(i); 
           } 
       } 
   }

   輸出：

   Queue is [User, Employee, Manager, Analyst, HR]
   The array created by toArray() is:
   User
   Employee
   Manager
   Analyst
   HR
   

2. toArray(T [] arr) 方法ArrayBlockingQueue類：
   ArrayBlockingQueue類的toArray(T [] a)方法用於創建一個數組，該數組包含與該ArrayBlockingQueue相同的元素，並且順序正確。它有一個附加條件。如果隊列大小小於或等於指定的數組，則返回的數組的類型與參數中指定的數組的類型相同。否則，將分配一個與指定數組相同類型的新數組，並且該數組的大小等於此隊列的大小。此方法充當數組和集合之間的橋梁。
   假設隊列是ArrayBlockingQueue，並且僅包含字符串。然後

   String[] new_arr = queue.toArray(new String[0]);

   請注意，toArray(new Object [0])與toArray()方法相同。

   用法:

   public  T[] toArray(T[] a)

   參數：該方法采用一個參數arr，該參數是一個數組，隊列中的所有元素(如果足夠大)都將複製到該數組中；否則，將為其分配相同運行時類型的新數組。

   返回值：該方法返回一個包含此隊列中所有元素的數組。

   異常：該方法可以引發以下異常之一：

   • ArrayStoreException：當傳遞的數組具有不同類型並且不能與隊列中的元素進行比較時。
   • NullPointerException ：如果數組為Null。

   下麵的程序說明ArrayBlockingQueue類的toArray(T [] a)方法：
   示例1:

   // Program Demonstrate how to apply toArray(T[] a) method 
   // of ArrayBlockingQueue Class. 
     
   import java.util.concurrent.ArrayBlockingQueue; 
     
   public class GFG { 
     
       public static void main(String[] args) 
       { 
           // Define capacity of ArrayBlockingQueue 
           int capacity = 5; 
     
           // Create object of ArrayBlockingQueue 
           ArrayBlockingQueue<String> queue = new 
                    ArrayBlockingQueue<String>(capacity); 
     
           // Add 5 elements to ArrayBlockingQueue 
           queue.offer("User"); 
           queue.offer("Employee"); 
           queue.offer("Manager"); 
           queue.offer("Analyst"); 
           queue.offer("HR"); 
     
           // Creating the array 
           String[] array = new String[5]; 
     
           // Calling toArray(T[] a) method 
           Object[] ReturnArray = queue.toArray(array); 
     
           // Print queue 
           System.out.println("Queue is " + queue); 
     
           // Print elements of array passed as parameter 
           System.out.println(); 
           System.out.println("The array passed to toArray() is:"); 
           for (Object i : array) { 
               System.out.println(i); 
           } 
     
           // Print elements of array retuned by method toArray() 
           System.out.println(); 
           System.out.println("The array retuned by toArray() is:"); 
           for (Object i : ReturnArray) { 
               System.out.println(i); 
           } 
       } 
   }

   輸出：

   Queue is [User, Employee, Manager, Analyst, HR]
   
   The array passed to toArray() is:
   User
   Employee
   Manager
   Analyst
   HR
   
   The array retuned by toArray() is:
   User
   Employee
   Manager
   Analyst
   HR
   

參考：

• https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ArrayBlockingQueue.html#toArray
• https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ArrayBlockingQueue.html#toArray-T:A