How to go to a specific activity?

How my application is structured...

Class A extends Activity {
    Button cButton = (Button) findViewById(...);
    Button dButton = (Button) findViewById(...);

    //invoked when cButton is clicked
    methodButtonC() { 
        //Here I want to go to the activity of class C and this is how I have tried to solve it...  
        Intent intent = new Intent(A.this, C.class);
        startActivity(intent);
    }
    //invoked when dButton is clicked
    methodButtonD() { 
         //Same problem as above but with Class D
    }
} 

// Base Class for C & D, No real purpose except sharing som methods to C & 开发者_开发问答D (should probobly be abstract?)
Class B extends A {  
    // vairables and methods for inheritance
} 

Class C extends B {
    // uses derived methods and variables from Class B
}

Class D extends B {
    // uses derived methods and variables from Class B
}

When I run the application and click the Button C or D error occurs. How shall I do it?

I would think you have to override the onCreate and load your view from xml by calling setContentView(...) before you try finding your buttons with findViewById(...)

@Override public void onCreate(Bundle savedInstanceState) 
{
  super.onCreate(savedInstanceState);
  setContentView(R.layout.<yourview>);

  buttonX = findViewById (...);
}