creating array of my class in "main"?

[sbooby2365]

I was reading the Java tutorial on arrays at
Arrays (The Java™ Tutorials > Learning the Java Language > Language Basics)

I can make an array of integers no problem. But when I try to make an array of my own class object, I get either a compile error or a run-time error.
It seems like I'm stuck if I do or if I don't…


Here's the code:



% cat Simple.java

public class Simple {

 private class MyType {
      int x;
 }
 
 public static void main(String[] args)  {   
 
            MyType[] myList;
            int[] intList;

            myList = new MyType[10];
            intList = new int[10];

            for (int n = 0; n < myList.length; n++) {
               System.out.println("n = "+n);
               intList[n] = 10;

             // The compiler does not like the next line.  Says "non-static variable this cannot be referenced from a static context"
              myList[n] = new MyType();
               myList[n].x = 1;
            }
  }
}

If I comment out the problematic line, then I get a run-time error at the "myList[n].x = 1;" line:

% java Simple
n = 0
Exception in thread "main" java.lang.NullPointerException
at Simple.main(Simple.java:20)



…And if I take out the "static" part of main, then the application won't run at all because it can't find the "main" method.


Any suggestions?
Thanks!

[Eranga]

What you have suppose to do on,

myList[n].x = 1;

[pbrockway2]

If I comment out the problematic line, then I get a run-time error at the "myList[n].x = 1;" line:

That makes sense because you aren't putting anything into the array, so myList[n] is null and the myList[n].x part will throw a NullPointerException.

And if I take out the "static" part of main, then the application won't run at all because it can't find the "main" method.

That also makes sense because the "static" is what allows the runtime to actually run main() before it ever has an instance of the Simple class. (if it ever does have one.)

-----

As for your problem itself, ... Why is MyType an inner class?

If you don't have a reason - and if you don't know what an inner class is, then you can't have a reason - my suggestion is that you take the definition of MyType out of the Simple class. It does not have to go in another file, you can put it in the same file, just outside Simple.

public class Foo {
    // stuff
}// <-- Foo finishes here

private class Bar {
    // more stuff
}

[diamonddragon]

What you have suppose to do on,

myList[n].x = 1;

Maybe to assign value to field of MyType object?

[Eranga]

Let see what OP thinks about that. However, pbrockway2 give a nice comment on his reply.