Question

我的代码中出现了java.lang.nullpointerexception错误。虽然我不确定为什么它不正确。我应该快速解决，但我似乎无法弄明白。似乎第45行中的数组给出了错误。任何帮助将不胜感激。提前谢谢。

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

class readFile
{
    private String fileName;
    private double lowestNum;
    private double highestNum;
    private double totalNum;
    private double averageNum;
    private int[] array;

    public readFile(String input)
    {
        fileName = input;
        lowestNum = 0;
        highestNum = 0;
        totalNum = 0;
        averageNum = 0;
    }

    public void readArray() throws FileNotFoundException
    {
        Scanner s = new Scanner(new File(fileName));
        array = new int[s.nextInt()];
        for(int i = 0; i < array.length; i++)
        {
            array[i] = s.nextInt();
        }
        s.close();
    }
    \\ERROR IS HERE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    public void findLowest()
    {
        lowestNum = array[0];
        for(int i = 1; i < array.length; i++)
        {
            if(array[i] < lowestNum);
            lowestNum = array[i];
        }
        System.out.println("Lowest number: " + lowestNum);
    }

    public void findHighest()
    {
        highestNum = array[0];
        for(int i = 1; i < array.length; i++)
        {
            if(array[i] > highestNum);
            highestNum = array[i];
        }
        System.out.println("Highest number: " + highestNum);
    }

    public void findTotalNum()
    {
        for(int i = 0; i < array.length; i++)
        {
            totalNum = totalNum + array[i];
        }
        System.out.println("Total of all numbers: " + totalNum);
    }

    public void findAverage()
    {
        averageNum = (totalNum / array.length);
        System.out.println("Average of all numbers: " + averageNum);
    }
}

public class NumberAnalysis 
{
    public static void main(String[] args) throws FileNotFoundException 
    {
        String fileName = "Numbers.txt";

        readFile myClass = new readFile(fileName);
        myClass.findLowest();
        myClass.findHighest();
        myClass.findTotalNum();
        myClass.findAverage();
    }
}

Answer 1

如果readArray()是设置数组的方法，则必须在尝试使用数组之前调用该方法。

Answer 2

您永远不会致电readArray，因此您的array永远不会被初始化。

Answer 3

问题是你实例化你的对象，但你忘记了实例化数组。你应该这样做：

public static void main(String[] args) throws FileNotFoundException 
{
    String fileName = "Numbers.txt";

    readFile myClass = new readFile(fileName);
    myClass.readArray();
    myClass.findLowest();
    myClass.findHighest();
    myClass.findTotalNum();
    myClass.findAverage();
}

顺便说一下，你应该总是有一个以大写字母开头的类，它会让你的代码更具可读性。

Answer 4

您必须调用readArray方法，并且还应该为其提供参数filename，以便Scanner可以获取参数filename。否则，它将生成FileNotFoundException

Java：＆＃34;线程主java.lang.nullpointerexception中的异常＃34;

4 个答案: