Java番石榴 |带有示例的 Doubles.toArray() 方法

Guava 库中Doubles 类的toArray()方法用于将作为参数传递给该方法的双精度值转换为双精度数组。这些双精度值作为集合传递给此方法。此方法返回一个 Double 数组。

句法：

public static double[] toArray(Collection collection)

参数：此方法接受一个强制参数集合，该集合是要转换为 Double 数组的双精度值的集合。

返回值：此方法以相同的顺序返回一个包含与集合相同的值的双精度数组。

异常：如果传递的集合或其任何元素为空，则此方法抛出NullPointerException 。

下面的程序说明了 toArray() 方法的使用：

示例 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 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]

示例 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 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 Java)