java - 如何将String[](数组)存储在String[][](数组的数组)中

Question

下面的代码给出了空指针异常

public class Testing {
    public static final String HD_DATA = "STOCK,D1,D2,D3,D4,D5,D6,D7,D8,D9,D10";
    public static final String HD_DATA_1 = "1,10,20,30,40,50,60,70,80,90,100";
    public static final String HD_DATA_2 = "2,11,22,33,44,55,66,77,88,99,111";
    public static void main(String[] args) {
        String[] hdDataArray = HD_DATA.split(",");
        String[] hdDataArray1 = HD_DATA_1.split(",");
        String[] hdDataArray2 = HD_DATA_2.split(",");
        String[][] pram = new String[3][];   //[null, null, null]

        for(int i=0;i<3;i++) {
            for(int j=0;j<hdDataArray.length;j++) {
                if(i ==0) {
                    pram[i][j] = hdDataArray[j]; // Exception in thread "main" java.lang.NullPointerException
                }
                else if (i ==1){
                    pram[i][j] = hdDataArray1[j];
                } else if(i == 2) {
                    pram[i][j] = hdDataArray2[j];
                }
            }
        }   
        System.out.println(pram);
    }
}

尝试给出时生成空指针异常，但我想在运行时插入数据有什么方法可以在运行时将数据插入数组数组中识别数组数组的大小，例如锯齿状数组

Answer 1

因为 pram = [null, null, null] ，因此 pram[i] (数组中位于 i 位置的数组) 当您通过 pram[i][j] 访问它时，它是 null。

public class Testing {
    public static final String HD_DATA = "STOCK,D1,D2,D3,D4,D5,D6,D7,D8,D9,D10";
    public static final String HD_DATA_1 = "1,10,20,30,40,50,60,70,80,90,100";
    public static final String HD_DATA_2 = "2,11,22,33,44,55,66,77,88,99,111";

    public static void main(String[] args) {
        String[] hdDataArray = HD_DATA.split(",");
        String[] hdDataArray1 = HD_DATA_1.split(",");
        String[] hdDataArray2 = HD_DATA_2.split(",");
        String[][] pram = new String[3][];   //[null, null, null]

        pram[0] = hdDataArray;
        pram[1] = hdDataArray1;
        pram[2] = hdDataArray2;

        System.out.println(pram);
    }
}