Web programming blog

Model–View–Controller (MVC) is an architectural pattern used in software engineering. It allows software developers to build a Web application as a composition of three roles: Model, View and Controller. A Model represents the state of a particular aspect of the application. Frequently, a model maps to a database table with the entries in the table representing the state of the table. A Controller handles interactions and updates the model to reflect a change in state of the application. A View extracts necessary information from a model and renders a user interface to display that”.<br/>

Here is the code for simple Calculator application written in Java which is organized according the the Model-View-Controller (MVC) pattern.<br/>

The main program initializes everything and ties everything together.

Main.java:

import javax.swing.*;

public class Main{
    public static void main(String[] args) {

        CalcModel      model      = new CalcModel();
        CalcView       view        = new CalcView(model);
        CalcController controller = new CalcController(model, view);

        view.setVisible(true);
    }
}

here is the View class:

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

class CalcView extends JFrame {
    private static final String INITIAL_VALUE = "1";

    private JTextField m_userInputTf = new JTextField(5);
    private JTextField m_totalTf     = new JTextField(20);
    private JButton    m_multiplyBtn = new JButton("Multiply");
    private JButton    m_clearBtn    = new JButton("Clear");

    private CalcModel m_model;

    CalcView(CalcModel model) {
        m_model = model;
        m_model.setValue(INITIAL_VALUE);

        m_totalTf.setText(m_model.getValue());
        m_totalTf.setEditable(false);

        JPanel content = new JPanel();
        content.setLayout(new FlowLayout());
        content.add(new JLabel("Input"));
        content.add(m_userInputTf);
        content.add(m_multiplyBtn);
        content.add(new JLabel("Total"));
        content.add(m_totalTf);
        content.add(m_clearBtn);

        //... finalize layout
        this.setContentPane(content);
        this.pack();

        this.setTitle("Simple Calc - MVC");

        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    void reset() {
        m_totalTf.setText(INITIAL_VALUE);
    }

    String getUserInput() {
        return m_userInputTf.getText();
    }

    void setTotal(String newTotal) {
        m_totalTf.setText(newTotal);
    }

    void showError(String errMessage) {
        JOptionPane.showMessageDialog(this, errMessage);
    }

    void addMultiplyListener(ActionListener mal) {
        m_multiplyBtn.addActionListener(mal);
    }

    void addClearListener(ActionListener cal) {
        m_clearBtn.addActionListener(cal);
    }
}

Here is the Controller class:

import java.awt.event.*;

public class CalcController {

    private CalcModel m_model;
    private CalcView  m_view;

    CalcController(CalcModel model, CalcView view) {
        m_model = model;
        m_view  = view;

        view.addMultiplyListener(new MultiplyListener());
        view.addClearListener(new ClearListener());
    }

    /*
     *  1. Get the user input number from the View.
     *  2. Call the model to mulitply by this number.
     *  3. Get the result from the Model.
     *  4. Tell the View to display the result.
     * If there was an error, tell the View to display it.
     */
    class MultiplyListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            String userInput = "";
            try {
                userInput = m_view.getUserInput();
                m_model.multiplyBy(userInput);
                m_view.setTotal(m_model.getValue());

            } catch (NumberFormatException nfex) {
                m_view.showError("Bad input: '" + userInput + "'");
            }
        }
    }
    class ClearListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            m_model.reset();
            m_view.reset();
        }
    }
}

and here is the Model class:

import java.math.BigInteger;

public class CalcModel {

    private static final String INITIAL_VALUE = "0";

    private BigInteger m_total;  // The total current value state.

    CalcModel() {
        reset();
    }

    public void reset() {
        m_total = new BigInteger(INITIAL_VALUE);
    }

    public void multiplyBy(String operand) {
        m_total = m_total.multiply(new BigInteger(operand));
    }

    public void setValue(String value) {
        m_total = new BigInteger(value);
    }

    public String getValue() {
        return m_total.toString();
    }
}

and here is the result:

have a nice day