You've declared the class Thing as a non-static inner class. That means it must be associated with an instance of the Hello class.
In your code, you're trying to create an instance of Thing from a static context. That is what the compiler is complaining about.
There are a few possible solutions. Which solution to use depends on what you want to achieve.
Move Thing out of the Hello class.
Change Thing to be a static nested class.
static class Thing
Create an instance of Hello before creating an instance of Thing.
public static void main(String[] args)
{
Hello h = new Hello();
Thing thing1 = h.new Thing(); // hope this syntax is right, typing on the fly :P
}
The last solution (a non-static nested class) would be mandatory if any instance of Thing depended on an instance of Hello to be meaningful. For example, if we had:
public class Hello {
public int enormous;
public Hello(int n) {
enormous = n;
}
public class Thing {
public int size;
public Thing(int m) {
if (m > enormous)
size = enormous;
else
size = m;
}
}
...
}
any raw attempt to create an object of class Thing, as in:
Thing t = new Thing(31);
would be problematic, since there wouldn't be an obvious enormous value to test 31 against it. An instance h of the Hello outer class is necessary to provide this h.enormous value:
...
Hello h = new Hello(30);
...
Thing t = h.new Thing(31);
...
Because it doesn't mean a Thing if it doesn't have a Hello.
For more information on nested/inner classes: Nested Classes (The Java Tutorials)