Java 中的 ConcurrentLinkedQueue toArray()方法
原文:https://www . geeksforgeeks . org/concurrentlinkedqueue-to array-method-in-Java/
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toArray() : The toArray() method of ConcurrentLinkedQueue is used to returns an array of the same elements as that of the ConcurrentLinkedQueue in proper sequence. Basically, it copies all the element from a ConcurrentLinkedQueue to a new array. This method behaves as a bridge between array and ConcurrentLinkedQueue.
语法:
java public Object[] toArray()返回:该方法返回一个数组，该数组包含类似于 ConcurrentLinkedQueue 的元素。
下面的程序说明了 Java . util . concurrentlinkedqueue . to array()方法。
例 1:
```java // Java Program Demonstrate toArray() // method of ConcurrentLinkedQueue
import java.util.concurrent.ConcurrentLinkedQueue;
public class GFG {
public static void main(String[] args) { // create object of ConcurrentLinkedQueue ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
// Add element to ConcurrentLinkedQueue queue.add(2300); queue.add(1322); queue.add(8945); queue.add(6512);
// print queue details System.out.println("Queue Contains " + queue);
// apply toArray() method on queue Object[] array = queue.toArray();
// Print elements of array System.out.println("The array contains:"); for (Object i : array) { System.out.print(i + "\t"); } } } ```
Output:
```java Queue Contains [2300, 1322, 8945, 6512] The array contains: 2300 1322 8945 6512
```
例 2:
```java // Java Program Demonstrate toArray() // method of ConcurrentLinkedQueue
import java.util.concurrent.ConcurrentLinkedQueue;
public class GFG { public static void main(String args[]) { // Creating a ConcurrentLinkedQueue ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
// elements into the Queue queue.add("Welcome"); queue.add("To"); queue.add("Jungle");
// Displaying the ConcurrentLinkedQueue System.out.println("The ConcurrentLinkedQueue: " + queue);
// Creating the array and using toArray() Object[] arr = queue.toArray();
System.out.println("The array is:"); for (int j = 0; j < arr.length; j++) System.out.println(arr[j]); } } ```
Output:
```java The ConcurrentLinkedQueue: [Welcome, To, Jungle] The array is: Welcome To Jungle
```
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toArray(T[] a) : The toArray(T[] a) method of ConcurrentLinkedQueue is used to an array containing the same elements as that of this ConcurrentLinkedQueue in proper sequence. This method differs from toArray() in only one condition. The type of the returned array is the same as the passed array in the parameter, if the ConcurrentLinkedQueue size is less than or equal to the passed array. Otherwise, a new array is allocated with the type same as the specified array and size of the array is equal to the size of this queue. This method behaves as a bridge between array and collections.
语法:
java public <T> T[] toArray(T[] a)参数:该方法以数组为参数，如果队列足够大，队列的所有元素都要复制到该参数中。否则，会为此分配一个相同运行时类型的新数组。
返回:这个方法返回包含类似于 ConcurrentLinkedQueue 元素的数组。
异常:该方法抛出以下异常:
- arraystorexception:当传递的数组与 ConcurrentLinkedQueue 的元素类型不同时。
- 空指针异常:如果传递的数组为空。
下面的程序说明了 Java . util . concurrentlinkedqueue . to array(T[]a)方法。
例 1:
```java // Java Program Demonstrate toArray() // method of ConcurrentLinkedQueue
import java.util.concurrent.ConcurrentLinkedQueue;
public class GFG {
public static void main(String[] args) { // create object of ConcurrentLinkedQueue ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
// elements into the Queue queue.add("Welcome"); queue.add("To"); queue.add("Jungle");
// print queue details System.out.println("Queue Contains " + queue);
// the array to pass in toArray() // array has size equal to size of ConcurrentLinkedQueue String[] passArray = new String[queue.size()];
// Calling toArray(T[] a) method Object[] array = queue.toArray(passArray);
// Print elements of passed array System.out.println("\nThe array passed :"); for (String i : passArray) { System.out.print(i + " "); }
System.out.println();
// Print elements of returned array System.out.println("\nThe array returned :"); for (Object i : array) { System.out.print(i + " "); } } } ```
Output:
```java Queue Contains [Welcome, To, Jungle]
The array passed : Welcome To Jungle
The array returned : Welcome To Jungle
```
例 2: 显示数组异常
```java // Java Program Demonstrate toArray() // method of ConcurrentLinkedQueue
import java.util.concurrent.ConcurrentLinkedQueue;
public class GFG {
public static void main(String[] args) { // create object of ConcurrentLinkedQueue ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
// Add element to ConcurrentLinkedQueue queue.add(2323); queue.add(2472); queue.add(4235); queue.add(1242);
// the array to pass in toArray() // array has size equal to size of ConcurrentLinkedQueue String[] passArray = new String[queue.size()];
// Calling toArray(T[] a) method try { Object[] array = queue.toArray(passArray); } catch (ArrayStoreException e) { System.out.println("Exception: " + e); } } } ```
Output:
```java Exception: java.lang.ArrayStoreException: java.lang.Integer
```
示例 2: 显示空指针异常
```java // Java Program Demonstrate toArray() // method of ConcurrentLinkedQueue
import java.util.concurrent.ConcurrentLinkedQueue;
public class GFG {
public static void main(String[] args) { // create object of ConcurrentLinkedQueue ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
// Add element to ConcurrentLinkedQueue queue.add(2323); queue.add(2472); queue.add(4235); queue.add(1242);
// the array to pass String[] passArray = null;
// Calling toArray(T[] a) method try { Object[] array = queue.toArray(passArray); } catch (NullPointerException e) { System.out.println("Exception: " + e); } } } ```
Output:
```java Exception: java.lang.NullPointerException
```
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