Java Guava Doubles.toArray()用法及代码示例

Guava库中Doubles Class的toArray()方法用于将作为参数传递给此方法的double值转换为Double Array。这些双精度值作为Collection传递给此方法。此方法返回一个Double数组。

用法:

public static double[] toArray(Collection<? extends Number> collection)

参数：此方法接受强制性参数集合，该参数集合是要转换为Double数组的double值的集合。

返回值：此方法以相同的顺序返回包含与集合相同的值的double数组。

异常：如果传递的集合或其任何元素为null，则此方法将引发NullPointerException。

以下示例程序旨在说明toArray()方法的使用：

范例1：

// Java code to show implementation of 
// Guava's Doubles.toArray() method 
  
import com.google.common.primitives.Doubles; 
import java.util.Arrays; 
import java.util.List; 
  
class GFG { 
  
    // Driver's code 
    public static void main(String[] args) 
    { 
  
        // Creating a List of Doubles 
        List<Double> myList 
            = Arrays.asList(1.2, 2.3, 3.4, 4.5, 5.6); 
  
        // Using Doubles.toArray() method to convert 
        // a List or Set of Double to an array of Double 
        double[] arr = Doubles.toArray(myList); 
  
        // Displaying an array containing each 
        // value of collection, 
        // converted to a double value 
        System.out.println(Arrays.toString(arr)); 
    } 
}

输出：

[1.2, 2.3, 3.4, 4.5, 5.6]

范例2：

// Java code to show implementation of 
// Guava's Doubles.toArray() method 
  
import com.google.common.primitives.Doubles; 
import java.util.Arrays; 
import java.util.List; 
  
class GFG { 
  
    // Driver's code 
    public static void main(String[] args) 
    { 
  
        try { 
            // Creating a List of Doubles 
            List<Double> myList 
                = Arrays.asList(1.2, 2.3, 3.4, null); 
  
            // Using Doubles.toArray() method 
            // to convert a List or Set of Double 
            // to an array of Double. 
            // This should raise "NullPointerException" 
            // as the collection contains "null" 
            // as an element 
            double[] arr = Doubles.toArray(myList); 
  
            // Displaying an array containing each 
            // value of collection, 
            // converted to a double value 
            System.out.println(Arrays 
                                   .toString(arr)); 
        } 
        catch (Exception e) { 
            System.out.println(e); 
        } 
    } 
}

输出：

java.lang.NullPointerException

参考：
https://google.github.io/guava/releases/19.0/api/docs/com/google/common/primitives/Doubles.html#toArray(java.util.Collection)

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注：本文由纯净天空筛选整理自Sahil_Bansall大神的英文原创作品 Java Guava | Doubles.toArray() method with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。