数组用null +元素填充

Question

我不知道为什么我的rows数组用null +我要放入的元素填充？

输出：nullelement，nullelement，nullelement

int numColumns = kbd.nextInt();

String columns = "";

kbd.nextLine();
for(int i = 0; i < numColumns; i++) {
    if (i == numColumns - 1) {
        System.out.printf("Enter Column %d: ", i + 1);
        columns += kbd.nextLine() + " VARCHAR(100)";
    } else {
        System.out.printf("Enter Column %d: ", i + 1);
        columns += kbd.nextLine() + " VARCHAR(100),";
    }
}
create(tableName, columns);
System.out.printf("\nHow many rows would you like your table to have? ");
int numRows = kbd.nextInt();
kbd.nextLine();
System.out.printf("\nFill in the %d columns: \n", numColumns);
String [] rows = new String[numColumns];

for(int i = 0; i < numRows; i++){
    for(int j = 0; j < numColumns; j++){
            System.out.printf("Enter Row %d: ", i + 1);
            rows[j] += kbd.nextLine();
    }
    write(tableName,rows);
    Arrays.fill(rows, null);
}

感谢您的见解和帮助！