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)

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

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
        }
    }