java queue toarray_Java PriorityBlockingQueue toArray()用法及代码示例

toArray()

PriorityBlockingQueue的toArray方法用于以适当的顺序创建一个数组，该数组具有与此PriorityBlockingQueue相同的元素。实际上，此方法将所有元素从PriorityBlockingQueue复制到新数组。此方法充当数组和PriorityBlockingQueue之间的桥梁。

用法:

public Object[] toArray()

返回值：此方法返回一个包含PriorityBlockingQueue元素的数组。

下面的程序说明PriorityBlockingQueue类的toArray()方法：

示例1:程序演示在PriorityBlockingQueue上使用toArray()方法从包含数字的PriorityBlockingQueue创建数字数组。

// Java Program Demonstrate toArray()

// method of PriorityBlockingQueue

import java.util.concurrent.PriorityBlockingQueue;

public class GFG {

public static void main(String[] args)

{

// define capacity of PriorityBlockingQueue

int capacityOfQueue = 5;

// create object of PriorityBlockingQueue

PriorityBlockingQueue PrioQueue

= new PriorityBlockingQueue(capacityOfQueue);

// Add numbers to PriorityBlockingQueue

PrioQueue.offer(35658786);

PrioQueue.offer(5278367);

PrioQueue.offer(74381793);

PrioQueue.offer(87625142);

// create an array of elements of PriorityBlockingQueue

Object[] array = PrioQueue.toArray();

// print elements of array

System.out.println(“Array Contains:”);

for (Object i : array) {

System.out.print(i + ” “);

}

}

}

输出：

Array Contains:

5278367 35658786 74381793 87625142

示例2:程序演示在PriorityBlockingQueue上使用toArray()方法从包含字符串值的PriorityBlockingQueue创建字符串数组。

// Java Program Demonstrate toArray()

// method of PriorityBlockingQueue

import java.util.concurrent.PriorityBlockingQueue;

import java.util.*;

public class GFG {

public static void main(String[] args)

{

// define capacity of PriorityBlockingQueue

int capacityOfQueue = 5;

// create object of PriorityBlockingQueue which contains

// name of students

PriorityBlockingQueue names

= new PriorityBlockingQueue(capacityOfQueue);

// Add names of students of girls college

names.offer(“Joyita”);

names.offer(“Bristi”);

names.offer(“Riya”);

// Create a array by calling toArray() method

Object[] array = names.toArray();

// Print List of names

System.out.println(“Queue is ” + names);

// Print elements of array

System.out.println(“The array created by toArray() is:”);

for (Object i : array) {

System.out.println(i + ” “);

}

}

}

输出：

Queue is [Bristi, Joyita, Riya]

The array created by toArray() is:

Bristi

Joyita

Riya

toArray(T[] a)

PriorityBlockingQueue的toArray(T [] a)方法用于按正确顺序返回包含与该PriorityBlockingQueue元素相同的元素的数组。此方法仅在一种情况下与toArray()不同。如果PriorityBlockingQueue大小小于或等于传递的数组，则返回的数组的类型与参数中传递的数组的类型相同。否则，将分配一个与指定数组相同类型的新数组，并且该数组的大小等于此队列的大小。此方法充当数组和集合之间的桥梁。

用法:

public T[] toArray(T[] a)

参数：此方法将数组作为参数，如果队列足够大，则要将队列的所有元素都复制到该数组中。否则，将为它分配一个具有相同运行时类型的新数组。

返回值：此方法返回一个包含此队列中所有元素的数组。

异常此方法引发以下异常：

ArrayStoreException：当传递的数组与PriorityBlockingQueue的元素类型不同时。

NullPointerException ：如果传递的数组为Null。

下面的程序说明PriorityBlockingQueue类的toArray(T [] a)方法：

示例1:该程序演示PriorityBlockingQueue上的toArray(T [] a)方法。

// Java Program Demonstrate toArray(T[] a)

// method of PriorityBlockingQueue

import java.util.concurrent.PriorityBlockingQueue;

import java.util.concurrent.TimeUnit;

public class GFG {

public static void main(String[] args)

throws InterruptedException

{

// define capacity of PriorityBlockingQueue

int capacityOfQueue = 3;

// create object of PriorityBlockingQueue

PriorityBlockingQueue PrioQueue

= new PriorityBlockingQueue(capacityOfQueue);

// Add names of students of girls college

PrioQueue.offer(“Joyi”);

PrioQueue.offer(“Rani”);

PrioQueue.offer(“Riya”);

// Creating the array

String[] array = new String[capacityOfQueue];

// Calling toArray(T[] a) method

Object[] ReturnArray = PrioQueue.toArray(array);

// Print queue

System.out.println(“Queue is ” + PrioQueue);

// 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);

}

}

}

输出：

Queue is [Joyi, Rani, Riya]

The array passed to toArray() is:

Joyi

Rani

Riya

The array retuned by toArray() is:

Joyi

Rani

Riya

示例2:演示由PriorityBlockingQueue的toArray(T [] a)方法引发的异常的程序。

// Java Program Demonstrate toArray(T[] a)

// method of PriorityBlockingQueue

import java.util.concurrent.PriorityBlockingQueue;

import java.util.concurrent.TimeUnit;

public class GFG {

public static void main(String[] args)

throws InterruptedException

{

// define capacity of PriorityBlockingQueue

int capacityOfQueue = 3;

// create object of PriorityBlockingQueue

PriorityBlockingQueue PrioQueue

= new PriorityBlockingQueue(capacityOfQueue);

// Add names of students of girls college

PrioQueue.offer(“Joyi”);

PrioQueue.offer(“Rani”);

PrioQueue.offer(“Riya”);

// Creating the array with null value

String[] array = null;

try {

// Calling toArray(T[] a) method

Object[] ReturnArray = PrioQueue.toArray(array);

}

catch (Exception e) {

System.out.println(“Exception thrown:” + e);

}

}

}

输出：

Exception thrown:java.lang.NullPointerException

参考：