java - 在Java中的类实例中初始化变量数组

Question

我有 C 语言背景，但在 Java 中遇到了问题。目前，我需要在一个对象数组中初始化一个变量数组。

我知道在 C 中它类似于 malloc-ing structs 数组中的 int 数组，例如:

typedef struct {
  char name;
  int* times;
} Route_t

int main() {
  Route_t *route = malloc(sizeof(Route_t) * 10);
  for (int i = 0; i < 10; i++) {
    route[i].times = malloc(sizeof(int) * number_of_times);
  }
...

到目前为止，在 Java 中我有

public class scheduleGenerator {

class Route {
        char routeName;
    int[] departureTimes;
}

    public static void main(String[] args) throws IOException {
      /* code to find number of route = numRoutes goes here */
      Route[] route = new Route[numRoutes];

      /* code to find number of times = count goes here */
      for (int i = 0; i < numRoutes; i++) {
        route[i].departureTimes = new int[count];
...

但它会吐出一个 NullPointerException。我做错了什么，是否有更好的方法来做到这一点？

Answer 1

初始化数组时

Route[] route = new Route[numRoutes];

numRoutes 个插槽都填充了它们的默认值。对于引用数据类型，默认值为 null，因此当您尝试在第二个 for 循环中访问 Route 对象时，它们都是 null，你首先需要像这样初始化它们:

public static void main(String[] args) throws IOException {
      /* code to find number of route = numRoutes goes here */
      Route[] route = new Route[numRoutes];

      // Initialization:
      for (int i = 0; i < numRoutes; i++) {
           route[i] = new Route();
      }

      /* code to find number of times = count goes here */
      for (int i = 0; i < numRoutes; i++) {
        // without previous initialization, route[i] is null here 
        route[i].departureTimes = new int[count];