Question

关于java从文本读取一个二维数组，然后简单计算，再写出的问题

文本：
78 87
78 78
54 78
现在在前面加！！！这句，会报空指针异常，不知道为什么

public class mysort {
public static void main(String[] args) throws FileNotFoundException,IOException{
int[][] aryBefore=getAry("myStudentScore.txt");
plusScore(aryBefore);
// ouputScore(aryBefore,"myStudentScore.txt");
}

private static void ouputScore(int[][] aryBefore, String string) {

}
private static void plusScore(int[][] aryBefore){
// System.out.println(aryBefore[0][0]);
int[] sum=new int[aryBefore.length];
for (int i = 0; i < aryBefore.length; i++) {
for (int j = 0; j < aryBefore[i].length; j++) {
sum[j]+=aryBefore[i][j];
}
}
System.out.println(Arrays.toString(sum));
}
private static int[][] getAry(String string) throws FileNotFoundException,IOException {
BufferedReader bufR=new BufferedReader(new FileReader(string));
String lineSrc;
int row=0;
int[][] getAry=new int[0][0];
while ((lineSrc=bufR.readLine())!=null) {
getAry=Arrays.copyOf(getAry, getAry.length+1);
String[] everScore=lineSrc.split(" ");
for (int i = 0; i < everScore.length; i++) {
！！！！ getAry[row]=Arrays.copyOf(getAry[row], getAry[row].length+1);
getAry[row][i]=Integer.parseInt(everScore[i]);
// System.out.println(getAry[row][i]+"+"+row);
row++;
}
lineSrc=bufR.readLine();
}
return getAry;
}
}

Answer 1

有两个问题：

1、叹号这一行里的 getAry[row] 没有初始化，所以NULL错误
2、row++应该在for循环外
我给你改了一下：

private static int[][] getAry(String string) throws FileNotFoundException, IOException {
BufferedReader bufR = new BufferedReader(new FileReader(string));
String lineSrc;
int row = 0;
int[][] getAry = new int[0][0];
while ((lineSrc = bufR.readLine()) != null) {
getAry = Arrays.copyOf(getAry, getAry.length + 1);
String[] everScore = lineSrc.split(" ");
getAry[row] = new int[0]; //这里先初始化一下getAry[row]，否则会报NULL错

for (int i = 0; i < everScore.length; i++) {
getAry[row] = Arrays.copyOf(getAry[row], getAry[row].length + 1);
getAry[row][i] = Integer.parseInt(everScore[i]);
// System.out.println(getAry[row][i]+"+"+row);
}
row++; //这个row++是行递增，应该在for之外
lineSrc = bufR.readLine();
}
return getAry;
}

Answer 2

你 这句代码 getAry=Arrays.copyOf(getAry, getAry.length+1);

取得getAry 是null 所以getAry[row] 就会报空指针异常了

Answer 3

数据下标是从0开始的，你用getAry[row].length+1会越界，把+1去掉吧

追问

但是，这不是吧原来的数组长度+1吗，

追答

数组的长度是不可变的，你要长度+1，要重新定义一个数组。
这样：int getAry2[row+1]=Arrays.copyOf(getAry[row], getAry[row].length+1);