Java Guava Doubles.toArray()用法及代碼示例

Guava庫中Doubles Class的toArray()方法用於將作為參數傳遞給此方法的double值轉換為Double Array。這些雙精度值作為Collection傳遞給此方法。此方法返回一個Double數組。

用法:

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

參數：此方法接受強製性參數集合，該參數集合是要轉換為Double數組的double值的集合。

返回值：此方法以相同的順序返回包含與集合相同的值的double數組。

異常：如果傳遞的集合或其任何元素為null，則此方法將引發NullPointerException。

以下示例程序旨在說明toArray()方法的使用：

範例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)); 
    } 
}

輸出：

[1.2, 2.3, 3.4, 4.5, 5.6]

範例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); 
        } 
    } 
}

輸出：

java.lang.NullPointerException

參考：
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：本文由純淨天空篩選整理自Sahil_Bansall大神的英文原創作品 Java Guava | Doubles.toArray() method with Examples。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。