Question

为什么这会给我Nullpointerexception的错误？它发生在我的代码的第3行，所以我的第一个循环。您知道，这是一种可以访问更大代码的其他部分的方法。

public static void insertionsort() 
{
    for (int outer = 1; outer < array.length; outer++)//Outer=next number to be sorted 
    { 
        String temp = array[outer]; //Stores it for later use
        int inner = outer; // inner used to track shifts 
        while (inner > 0 && array[inner - 1].compareTo(temp) >= 0) 
        {  
            array[inner] = array[inner - 1];//Swaps the number
            inner--;// Decrements
        } //shift them all right until one is smaller 
        array[inner] = temp;//Now it will put the stored number into its ordered position. 
    }
}

Answer 1

此行中未定义变量array

for (int outer = 1; outer < array.length; outer++)//Outer=next number to be sorted

如果这是一个函数参数，那么像这样添加它

public static void insertionsort(int[] array) 
{
     for (int outer = 1; outer < array.length; outer++)//Outer=next number to be sorted

或在

中定义

public static void insertionsort() 
{

    int[] array = {2,1,4,7,6,3};

    for (int outer = 1; outer < array.length; outer++)//Outer=next number to be sorted

Answer 2

我刚刚创建了一个单元测试来重现NPE，但我没有收到任何错误。我的建议是将fortetece分成多行，这样你就可以得到NPE的确切位置。

    for (int outer = 1; 
            outer < array.length; 
            outer++)//Outer=next number to be sorted 
    {

完整的单元测试是：

package src.test.java;  
import org.junit.Test;

public class TestOne {


   private static String[] array={"sa","se","si","so", "su"};
   @Test
   public void TestOne(){
    this.insertionsort();
   }

   public static void insertionsort() 
   {
    for (int outer = 1; 
            outer < array.length; 
            outer++)//Outer=next number to be sorted 
    { 
        String temp = array[outer]; //Stores it for later use
        int inner = outer; // inner used to track shifts 
        while (inner > 0 && array[inner - 1].compareTo(temp) >= 0) 
        {  
            array[inner] = array[inner - 1];//Swaps the number
            inner--;// Decrements
        } //shift them all right until one is smaller 
        array[inner] = temp;//Now it will put the stored number into its ordered position. 
    }
}

}

它告诉我NullPointerexception的原因

2 个答案: