How to solve the problem of java,lang.NullPointerException in MVC based java program

I am creating a MVC based simple addition program in Java for learning purposes. It's like a calculator with three text fields and a button. In two fields we enter two numbers to add and on clicking the button the result is displayed in third field (Similar to this: A + B = C). Here, A and B are those two input field and C is the text field where result is displayed. It compiled successfully but showing an error during run time, which is as follow:

Exception in thread "main" java.lang.NullPointerException
    at CalculatorView.launchUI(CalculatorView.java:42)
    at CalculatorController.<init>(CalculatorController.java:12)
    at Calculator.main(Calculator.java:5)

I am developing it in NetBeans IDE and tried to insert break-points at respective lines shown in error message to observe what was happening. The observation was something like this:

program control jumps from line 5 in Calculator.java to line 12 CalculatorController.java from there it goes to line 42 in CalculateView.java and then suddenly error is shown! I tried to comment that line then the error is shown like this:

..at CalculatorView.launchUI(CalculatorView.java:43)

I tried commenting this line also but then the next line is shown in error. I was able to comment these three lines because they were statements about the layout which are not affecting the internal logic and overall execution of program. I spent hours and could not find out what is actually wrong with this program. I tried to read about exception handling but still got failed in finding the problem.

Note: I am beginner in Java and knows nothing about exception handling and debugging process in particular.

I am uploading my code here. I have made 4 files: CalculatorModel.java, CalculatorView.java, CalculatorController.java and Calculator.java (main is located here). I am merging the code of all 4 files together and marking down when one file ends and other begins...

Note: The order of merging these programs are as follow:

1. Import statements


2. CalculatorModel.java


3. CalculatorView.java (Error Line 42 is here, I've mentioned it in comment)


4. CalculatorController.java (Error Line 12 is here)


5. 
   

   Calculator.java (Error Line 5 is here)

   
   

   
   import java.awt.*;
   import java.awt.event.*;
   import java.awt.BorderLayout;
   import java.awt.FlowLayout;
   import java.awt.GridLayout;
   
   
   /********* CalculatorModel.java BEGINS **********/
   
       public class CalculatorModel{
           private double numOne;  
           private double numTwo;
           private double addResult;
   
           public void addition(double one, double two){
               addResult = one + two;
           }
   
           public double getAddResult(){
               return addResult;
           }
       }
   
       /******** ENDOF CalculatorModel.java **********/
   
       /********* CalculatorView.java BEGINS **********/
   
       public class CalculatorView{
           //Declaring refrences for components to use
           private Frame f;
   
           private TextField inputFieldOne;
           private TextField inputFieldTwo;
           private TextField inputFieldThree;
   
           private Label labelPlus;
           private Label labelEquality;
   
           private Panel rowOne;
           private Panel rowTwo;
   
           private Button buttonAdd;
   
           //Parameterized constructor to initialize refrences with their respective objects
           public CalculatorView(String title){
               f = new Frame(title);
   
               inputFieldOne = new TextField(10);
               inputFieldTwo = new TextField(10);
               inputFieldThree = new TextField(10);
   
               labelPlus = new Label("+");
               labelEquality = new Label("=");
   
               buttonAdd = new Button("Add");
           }
   
           //Method to launch the User Interface/UI
           public void launchUI(){
   
               //Setting the layout
               f.setLayout(new BorderLayout());
               rowOne.setLayout(new GridLayout(1, 5)); //<----THIS IS LINE 42
               rowTwo.setLayout(new FlowLayout());
   
               //Adding the components to their respective layout
               //Adding input fields and labels in rowOne panel
               rowOne.add(inputFieldOne);
               rowOne.add(labelPlus);
               rowOne.add(inputFieldTwo);
               rowOne.add(labelEquality);
               rowOne.add(inputFieldThree);
   
               //Adding button in rowTwo panel
               rowTwo.add(buttonAdd);
   
               //Adding rowOne and rowTwo panels on the frame
               f.add(rowOne, BorderLayout.NORTH);
               f.add(rowTwo, BorderLayout.CENTER);
   
               f.setSize(200, 300);
               f.setVisible(true);
           }
   
           //Method to GET VALUE of TextField "inputFieldOne" in double format
           public double getInputFieldOne(){
               return (Double.parseDouble(inputFieldOne.getText()));
           }
   
           //Method to GET VALUE of TextField "inputFieldTwo" in double format
           public double getInputFieldTwo(){
               return (Double.parseDouble(inputFieldTwo.getText()));
           }
   
           //Method to SET VALUE of TextField "inputFieldOne" in double format
           public void setInputFieldThree(double valueToSet){
               inputFieldThree.setText(String.valueOf(valueToSet));
           }
   
           //Attaching the ActionListeners to their respective components
           //SET ActionListener to Button
           public void setButtonActionListener(ActionListener al){
               buttonAdd.addActionListener(al);
           }
   
           //SET WindowListener to Frame
           public void setFrameWindowListener(WindowListener wl){
               f.addWindowListener(wl);
           }
       }
   
       /******** ENDOF CalculatorView.java **********/
   
       /********* CalculatorController.java BEGINS **********/
   
       public class CalculatorController{
           private CalculatorModel model; 
           private CalculatorView view; 
   
           public CalculatorController(CalculatorModel model, CalculatorView view){
               this.model = model;
               this.view = view;
   
               this.view.launchUI(); //<----THIS IS LINE 12
               this.view.setButtonActionListener(new ActionHandler());
               this.view.setFrameWindowListener(new WindowHandler());
           }
   
           //Inner class IMPLEMENTING ActionListener
           public class ActionHandler implements ActionListener{
               public void actionPerformed(ActionEvent ae){
                   model.addition(view.getInputFieldOne(), view.getInputFieldTwo());
                   view.setInputFieldThree(model.getAddResult());
               }
           } 
   
           //Inner class EXTENDING WindowAdapter
           public class WindowHandler extends WindowAdapter{
               public void windowClosing(WindowEvent we){
                   System.exit(0);
               }
           }
       }
   
       /******** ENDOF CalculatorController.java **********/
   
       /********* Calculator.java BEGINS **********/
   
       public class Calculator{
           public static void main(String args[]){
               CalculatorModel model = new CalculatorModel();
               CalculatorView view = new CalculatorView("Calculator");
               CalculatorController controller = new CalculatorController(model, view); //<----THIS IS LINE 5
           }
       }
   
   

Please help me in pin pointing the exact problematic area in the program and why it is creating error. In addition what are the steps should I follow to solve this?