No enclosing instance of type test is accessible | Java

Below code will give error No enclosing instance of type test is accessible. Must qualify the allocation with an enclosing instance of type test (e.g. x.new A() where x is an instance of test).

class Hello { 

  class Thing { 
    public int size; 
    
    Thing() { 
      size = 0; 
    }
  } 
  
  public static void main(String[] args) { 
  
    Thing thing1 = new Thing(); // This will give above error 
    System.out.println("Hello, World!"); 
  }
}

Thing is an inner class, which (by definition) is associated with a particular instance of Hello (even if it never uses or refers to it), which means it’s an error to say new Thing(); without having a particular Hello instance in scope. If you declare it as a static class instead, then it’s a “nested” class, which doesn’t need a particular Hello instance. So in code, creating an instance of Thing from a static context is throwing error.