读取文件并放入数组

I'm having troubles reading a file and then placing its contents into an array. The console says my error is here:

我在阅读文件然后将其内容放入数组时遇到麻烦。控制台说我的错误在这里:

Exception in thread "main" java.lang.NullPointerException
at readFile.readFile(readFile.java:23)
at apples.main(apples.java:6)

However I do not now how to fix it.

但是我现在不知道如何解决它。

import java.util.*;
import java.lang.*;
import java.io.*;


public class readFile {
private Scanner x;

public void openfile(){
    try{
        x = new Scanner( new File("/Users/Zachary/Desktop/chinese.txt"));

    }
    catch (IOException e){
        System.out.println("you failed foo");
    }
}
    public void readFile(){
        int y = 0;
        int[] nums = null;
        while(x.hasNext()){
            for(y=0; y<10;y++) {
                nums[y] = x.nextInt();
            }
            System.out.println(nums[y]);
        }
    }
    public void closeFile(){
        x.close();
    }
}



public class apples {
public static void main (String[]args){
    readFile r = new readFile();
    r.openfile();
    r.readFile();
    r.closeFile();

}
}

3 个解决方案

#1

You seem to have a NullPointerException at:

您似乎在以下位置有NullPointerException:

nums[y] = x.nextInt();

That is because of this line:

那是因为这条线:

int[] nums = null;

It is null, so you can't put stuff in it. Here's a simple fix:

它是null,所以你不能把东西放进去。这是一个简单的修复:

int[] nums = new int[10];

The above code will initialize nums so that it is an empty (not really - it's actually filled with 0) array like this:

上面的代码将初始化nums,以便它是一个空的(不是真的 - 它实际上填充了0)数组,如下所示:

---------------------
|0|0|0|0|0|0|0|0|0|0|
---------------------

If you want to be able to add as many numbers to it as you want, you will need an ArrayList (link).

如果您希望能够根据需要添加任意数量的数字,则需要一个ArrayList(链接)。

Also, this code will throw an error:

此外,此代码将引发错误:

for(y=0; y<10;y++) {
    nums[y] = x.nextInt();
}
System.out.println(nums[y]);

That is because your System.out.println doesn't know what y is. Just move the System.out.println into the for loop so it can "see" y. (This is called scope)

那是因为你的System.out.println不知道y是什么。只需将System.out.println移动到for循环中,就可以“看到”y。 (这称为范围)

#2

The compiler error states that the error occurs at "readFile.java:23". This is line 23 of the file readFile.java. I believe that is this line:

编译器错误表明错误发生在“readFile.java:23”。这是文件readFile.java的第23行。我相信这就是这条线:

nums[y] = x.nextInt();

The problem is that you declared nums as:

问题是您将nums声明为:

int[] nums = null;

When you try to access an array that is initialized to null, you should not be surprised to get a NullPointerException.

当您尝试访问初始化为null的数组时,您不应对获得NullPointerException感到惊讶。

To fix the problem, you need to create an array object:

要解决此问题,您需要创建一个数组对象:

int[] nums = new int[SOME_SIZE];

You will need to provide the size yourself as you have not provided enough information for me to guess the value.

您需要自己提供尺寸,因为您没有提供足够的信息来猜测我的价值。

#3

is the inner loop really necessary? you are looping x * 10 times which is really not a good way to assigned data.

内循环真的有必要吗?你循环x * 10次,这实际上不是分配数据的好方法。

#1