Two common minor problems of cross-border and array operations null pointer

Two common minor problems of cross-border and array operations null pointer:

• a: ArrayIndexOutOfBoundsException: Array index out of bounds abnormal
  • The reason: you visit the index does not exist.
  • int[] arr = new int[3];
  • System.out.println(arr[3]);
• b: NullPointerException: null pointer exception
  • The reason: no longer pointing to an array of heap memory. And you also use to access the elements of an array name.
  • int[] arr = {11,12,13};
  • scar = null;
  • System.out.println(arr[0]);