Java Guava Ints toArray()用法及代碼示例

Guava的Ints.toArray()返回包含每個collection值的數組，並以Number.intValue()的方式轉換為int值

用法:

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

參數：此方法將集合作為參數，它是Number實例的集合。

返回值：此方法返回一個數組，該數組包含與collection相同的值，並以相同順序轉換為基元。

異常：如果collection或其任何元素為null，則此方法將引發NullPointerException。

以下示例說明了Ints.toArray()方法：

範例1：

// Java code to show implementation of 
// Guava's Ints.toArray() method 
  
import com.google.common.primitives.Ints; 
import java.util.Arrays; 
import java.util.List; 
  
class GFG { 
  
    // Driver's code 
    public static void main(String[] args) 
    { 
  
        // Creating a List of Integers 
        List<Integer> 
            myList = Arrays.asList(1, 2, 3, 4, 5); 
  
        // Using Ints.toArray() method to convert 
        // a List or Set of Integer to an array 
        // of Int 
        int[] arr = Ints.toArray(myList); 
  
        // Displaying an array containing each 
        // value of collection, 
        // converted to a int value 
        System.out.println("Array from given List:"
                           + Arrays.toString(arr)); 
    } 
}

輸出：

Array from given List:[1, 2, 3, 4, 5]

範例2：演示NullPointerException

// Java code to show implementation of 
// Guava's Ints.toArray() method 
  
import com.google.common.primitives.Ints; 
import java.util.Arrays; 
import java.util.List; 
  
class GFG { 
  
    // Driver's code 
    public static void main(String[] args) 
    { 
  
        try { 
  
            // Creating a List of Integers 
            List<Integer> 
                myList = Arrays.asList(2, 4, null); 
  
            // Using Ints.toArray() method to convert 
            // a List or Set of Integer to an array 
            // of Int. This should raise "NullPointerException" 
            // as the collection contains "null" as an element 
            int[] arr = Ints.toArray(myList); 
  
            // Displaying an array containing each 
            // value of collection, converted to a int value 
            System.out.println(Arrays.toString(arr)); 
        } 
        catch (Exception e) { 
            System.out.println("Exception:" + e); 
        } 
    } 
}

輸出：

Exception:java.lang.NullPointerException

參考： https://google.github.io/guava/releases/22.0/api/docs/com/google/common/primitives/Ints.html#toArray-java.util.Collection-

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