Guava Ints toArray() 函数

Guava的 Ints .toArray() 返回一个包含集合中每个值的数组，以Number.intValue()的方式转换为int值

语法:

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

参数： 这个方法以集合为参数，它是Number实例的集合。

返回值 这个方法返回一个数组，包含与集合相同的值，以相同的顺序转换为基数。

异常情况。 如果集合或其任何元素为空，该方法会抛出NullPointerException。

下面的例子说明了Ints.toArray()方法。

示例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));    }}

输出:

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

示例2: 要演示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);        }    }}

输出:

Exception: java.lang.NullPointerException

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