我如何组织我的Java代码？

Question

The title is not my entire question. I know HOW to organize code, theoretically, but i would like some specific, USEFUL, pointers. Please read on before griping.

I'm a beginner to java and OOP (object oriented programming) and I would really like to learn how to better organize my code! Over the course of a month or two, I made a calculator program with little functions I thought of here and there with a few small jokes built into it. After looking at it a second time I realized that it is extremely poorly formatted and almost incomprehensible.If I may, I would like to ask some more experienced programmers to point me in the right direction on what I should do to fix it (for example, what things can I turn into objects, Where can I compartmentalize, etc).

Please note that this is my FIRST time posting on a forum like this so if i need to clarify something for you to help me, I've done something wrong, I'm asking for too much, please tell me so i can resolve it and i can get help. Please dont just mark this as invalid and file it away to oblivion (as often happens in stackoverflow). Also, before anyone asks, NO this is NOT homework, it is the product of my own crack at teaching myself java (probably why its not working too well).

Here is the source code:

// This is the original Calculator code without objects in a single class. not really efficient...
package randomClasses;
import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;
import javax.swing.*;

@SuppressWarnings("serial")
public class CalcClass
        extends JFrame
        implements ActionListener {
    JPanel[] row = new JPanel[6];
    JButton[] button = new JButton[21];
    String[] buttonString = {"7", "8", "9", "+", "4", "5", "6", "-", "1", "2", "3", "*", ".", "/", "C", "v", "+/-", "=", "0", "Parabola", "x^y"};
    int[] dimW = {300, 45, 100, 90, 180};
    int[] dimH = {35, 40};
    Dimension displayDimension = new Dimension(dimW[0], dimH[0]);
    Dimension regularDimension = new Dimension(dimW[1], dimH[1]);
    Dimension rColumnDimension = new Dimension(dimW[2], dimH[1]);
    Dimension zeroButDimension = new Dimension(dimW[3], dimH[1]);
    Dimension parabolaDimension = new Dimension(dimW[4], dimH[0]);
    //formatting variables
    int var = 0;
    double x = 0;
    String stor = "";
    boolean initial = true;
    //variables for Parabola function
    int countEquals_parab = 0;
    double Angle = 0;
    double Vi = 0;
    double Vx = 0;
    double Vy = 0;
    double T_max = 0;
    double Y_displ = 0;
    double X_displ = 0;
    double h = 0;
    double k = 0;
    double a_parab = 0;
    boolean parabComplete = true;
    boolean parabola = false;
    DecimalFormat df = new DecimalFormat("#######.#####");
    //variables for addressing illegal typing issues
    boolean typeNum = true;
    boolean typeDot = true;
    JFrame frame; //for parabolaInstructions
    //original calculator variables
    boolean[] function = new boolean[5];
    double[] temporary = {0, 0}; //store on screen values
    double result = 0; //store result
    public JTextArea display = new JTextArea(1, 20);
    Font font = new Font("Times new Roman", Font.BOLD, 14);

    CalcClass() {
        super("CalcClass");
        setDesign();
        setSize(380, 300);
        setResizable(false);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        GridLayout grid = new GridLayout(6, 5);
        setLayout(grid);
        for(int i = 0; i < 5; i++) {
            function[i] = false;
        }
        FlowLayout f1 = new FlowLayout(FlowLayout.CENTER);
        FlowLayout f2 = new FlowLayout(FlowLayout.CENTER, 1, 1);
        for(int i = 0; i < 6; i++) {
            row[i] = new JPanel();
        }
        row[0].setLayout(f1);
        for(int i = 1; i < 6; i++) {
            row[i].setLayout(f2);
        }
        for(int i = 0; i < 21; i++) {
            button[i] = new JButton();
            button[i].setText(buttonString[i]);
            button[i].setFont(font);
            button[i].addActionListener(this);
        }
        display.setFont(font);
        display.setEditable(false);
        display.setPreferredSize(displayDimension);
        for(int i = 0; i < 14; i++) {
            button[i].setPreferredSize(regularDimension);
        }
        for(int i = 14; i < 18; i++) {
            button[i].setPreferredSize(rColumnDimension);
        }
        button[18].setPreferredSize(zeroButDimension);
        button[19].setPreferredSize(parabolaDimension);
        button[20].setPreferredSize(rColumnDimension);
        row[0].add(display);
        add(row[0]);
        for(int i = 0; i < 4; i++) {
            row[1].add(button[i]);
        }
        row[1].add(button[14]);
        add(row[1]);
        for(int i = 4; i < 8; i++) {
            row[2].add(button[i]);
        }
        row[2].add(button[15]);
        add(row[2]);
        for(int i = 8; i < 12; i++) {
            row[3].add(button[i]);
        }
        row[3].add(button[16]);
        add(row[3]);
        row[4].add(button[18]);
        for(int i = 12; i < 14; i++) {
            row[4].add(button[i]);
        }
        row[4].add(button[17]);
        add(row[4]);
        row[5].add(button[19]);
        row[5].add(button[20]);
        add(row[5]);
        setVisible(true);
    }

    public void getSqrt() {
        stor = "";
        initial = true;
        try {
            double value = Double.parseDouble(display.getText());
            if(value == -100) {
                format("John's Girlfriend");
            } else {
                value = Math.sqrt(Double.parseDouble(display.getText())); //create a value for variable, and use Maths square root to find the value
                format(Double.toString(value)); //Sets display to new value
            }
        } catch(NumberFormatException e) {
        }
        typeDot = false;
        typeNum = false;
    }

    public void getPosNeg() {
        stor = "";
        initial = true;
        try {
            double value = Double.parseDouble(display.getText()); //again creating a variable for current value
            if(value != 0) { //if value is not equal to zero
                value = (-1) * value; //multiplied by -1 to change the sign
                format(Double.toString(value)); //Sets display to new value
            } else {
            }
        } catch(NumberFormatException e) {
        }
    }

    public void getResult() {
        temporary[1] = Double.parseDouble(display.getText());
        String temp0 = Double.toString(temporary[0]);
        String temp1 = Double.toString(temporary[1]);
        try {
            if(temp0.contains("-")) {
                String[] temp00 = temp0.split("-", 2);
                temporary[0] = (Double.parseDouble(temp00[1]) * -1);
            }
            if(temp1.contains("-")) {
                String[] temp11 = temp1.split("-", 2);
                temporary[1] = (Double.parseDouble(temp11[1]) * -1);
            }
        } catch(ArrayIndexOutOfBoundsException e) {
        }
        try {
            functions();
            clear();
            format(Double.toString(result));//display has a result
            for(int i = 0; i < 5; i++) {
                function[i] = false; //set all functions to false
            }
        } catch(NumberFormatException e) {
        }
        typeNum = false;
    }

    public void functions() {
        if(function[2] == true) { //multiplication 
            result = temporary[0] * temporary[1];
        } else if(function[3] == true) { //division
            result = temporary[0] / temporary[1];
        } else if(function[0] == true) { //addition
            result = temporary[0] + temporary[1];
        } else if(function[1] == true) { //subtraction;
            result = temporary[0] - temporary[1];
        } else if(function[4] == true) {
            result = Math.pow(temporary[0], temporary[1]);
        } else {
            result = temporary[1];
        }
    }

    double a_quadratic = 0;
    double b = 0;
    double c = 0;
    double x1 = 0;
    double x2 = 0;
    double discr = 0;
    int countEquals_quadratic = 0;

    public void quadraticFormula() {
        if(countEquals_parab == 0) {
            a_quadratic = Double.parseDouble(display.getText());
            clear();
            display.setText("b = ");
        }
        if(countEquals_parab == 1) {
            b = Double.parseDouble(display.getText());
            display.setText("c = ");
        }
        if(countEquals_parab == 2) {
            c = Double.parseDouble(display.getText());
            discr = (Math.pow(b, 2) - 4 * a_quadratic * c); //stores the value of the discriminant
            if(discr >= 0) {
                x1 = (-b + Math.sqrt(b * b - 4 * a_quadratic * c)) / (2 * a_quadratic);
                x2 = (-b - Math.sqrt(b * b - 4 * a_quadratic * c)) / (2 * a_quadratic);
            }
        }
    }

    public void parabolaButton() {
        double G = 9.81;
        if(countEquals_parab == 0) {
            Vi = Double.parseDouble(display.getText());
            clear();
            display.setText("Angle of release: ");
        }
        if(countEquals_parab == 1) {
            Angle = Double.parseDouble(display.getText());
            if((Angle > 90.0) || (Angle < 0.0)) {
                display.setText("Sorry, not a valid angle");
                countEquals_parab = 3;
            } else {
                Angle = (Math.PI / 180.0) * Angle;  //converting degrees into radians
                Vx = Vi * Math.cos(Angle); //Calculating x component
                Vy = Vi * Math.sin(Angle); //Calculating y component
                //Finding time
                T_max = Vy / G; //time to max height
                //Calculating vertex coordinates
                Y_displ = (Vy * Vy / (2 * G));
                X_displ = Vx * T_max;
                //finding a
                a_parab = (-Y_displ) / (X_displ * X_displ);
                display.setText("The equation of the parabola is \ny = " + df.format(a_parab) + "(x - " + df
                        .format(h) + ")^2 + " + df.format(k));
            }
        }
        if(countEquals_parab == 2) {
            display.setText("Time to get to max height = " + df.format(T_max));
        }
        if(countEquals_parab == 3) {
            clearFunction();
            countEquals_parab = -1;
            parabola = false;
            parabComplete = true;
        }
        countEquals_parab++;
    }

    public void var() {
        var++;
        if(var > 8) {
            var = 1;
        }
        if(var == 1) {
            format("x");
        }
    }

    public final void setDesign() {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch(Exception e) {
        }
    }

    public void format(String get) {
        //get stores the incoming values temporarily
        //get is transferred to a new value for permanent storage
        //print the permanent storage value
        //new number is added, stored temporarily in get
        //get is added to permanent storage
        //print permanent storage value
        double spaceFix = 0;
        if(initial == true) {
            stor = get;
            initial = false;
        } else if(initial == false) {
            stor = stor + get;
        }
        spaceFix = stor.length() / 4;
        int numberOfSpaces = 56 - stor.length() + (int) spaceFix;
        String format = String.format("%" + numberOfSpaces + "s", stor);
        display.setText(format);
    }

    @Override
    public void actionPerformed(ActionEvent ae) {
        if(ae.getSource() == button[0]) {
            numberButtons("7");
        }
        if(ae.getSource() == button[1]) {
            numberButtons("8");
        }
        if(ae.getSource() == button[2]) {
            numberButtons("9");
        }
        if(ae.getSource() == button[3]) {
            operatorButtons(0); //add function[0]
        }
        if(ae.getSource() == button[4]) {
            numberButtons("4");
        }
        if(ae.getSource() == button[5]) {
            numberButtons("5");
        }
        if(ae.getSource() == button[6]) {
            numberButtons("6");
        }
        if(ae.getSource() == button[7]) {
            operatorButtons(1); //subtract function[1]
        }
        if(ae.getSource() == button[8]) {
            numberButtons("1");
        }
        if(ae.getSource() == button[9]) {
            numberButtons("2");
        }
        if(ae.getSource() == button[10]) {
            numberButtons("3");
        }
        if(ae.getSource() == button[11]) {
            operatorButtons(2); //multiplication function[2]
        }
        if(ae.getSource() == button[12]) {
            if(typeDot == false) {
            } else {
                numberButtons(".");
                typeDot = false;
            }
        }
        if(ae.getSource() == button[13]) {
            operatorButtons(3); //divide function[3]
        }
        if(ae.getSource() == button[14]) {
            clearFunction();
            parabola = false;
            parabComplete = true;
        }
        if(ae.getSource() == button[15]) {
            getSqrt();
        }
        if(ae.getSource() == button[16]) {
            getPosNeg();
        }
        if((ae.getSource() == button[17]) && display.getText().equals("")) {
        } else if((ae.getSource() == button[17]) && (parabola == false)) {
            getResult();
        } else if((ae.getSource() == button[17]) && (parabola == true)) {
            parabolaButton();
        }
        if(ae.getSource() == button[18]) {
            numberButtons("0");
        }
        if(ae.getSource() == button[19]) {
            clearFunction();
            parabolaInstructions();
            parabola = true;
            parabComplete = false;
            display.setText("Initial velocity: ");
        }
        if(ae.getSource() == button[20]) {
            operatorButtons(4);//powerFunction();
        }
    }

    public void parabolaInstructions() {
        //Create the dialog.
        final JDialog dialog = new JDialog(frame, "How to use the Parabola function");
        //Add contents to it. It must have a close button,
        //since some L&Fs (notably Java/Metal) don't provide one
        //in the window decorations for dialogs.
        JLabel label = new JLabel("<html><p align=center>" + "Step 1:  Type in the initial velocity and press the \"=\" button<br>" + "Step 2:  Type in the angle of Release (make sure that it is between 0 and 90)<br>" + "Step 3:  Press the \"=\" button to scroll through the results<br>" + "Step 4:  Profit");
        label.setHorizontalAlignment(JLabel.CENTER);
        Font font = label.getFont();
        label.setFont(label.getFont().deriveFont(font.PLAIN, 14.0f));
        JButton closeButton = new JButton("Ok");
        closeButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                dialog.setVisible(false);
                dialog.dispose();
            }
        });
        JPanel closePanel = new JPanel();
        closePanel.setLayout(new BoxLayout(closePanel, BoxLayout.LINE_AXIS));
        closePanel.add(Box.createHorizontalGlue());
        closePanel.add(closeButton);
        closePanel.setBorder(BorderFactory.
                createEmptyBorder(0, 0, 5, 5));
        JPanel contentPane = new JPanel(new BorderLayout());
        contentPane.add(label, BorderLayout.CENTER);
        contentPane.add(closePanel, BorderLayout.PAGE_END);
        contentPane.setOpaque(true);
        dialog.setContentPane(contentPane);
        //Show it.
        dialog.setSize(new Dimension(400, 200));
        dialog.setLocationRelativeTo(frame);
        dialog.setVisible(true);
    }

    public void numberButtons(String i) {
        if(typeNum == false) {
            display.setText("");
            format(i);
        } else {
            format(i);
        }
        typeNum = true;
    }

    public void operatorButtons(int funct) {
        if(display.getText().equals("")) {
        } else {
            temporary[0] = Double.parseDouble(display.getText());
            function[funct] = true;
            clear();
        }
    }

    public void clearFunction() {
        clear();
        try {
            for(int i = 0; i < 5; i++) {
                function[i] = false;
            }
            for(int i = 0; i < 2; i++) {
                temporary[i] = 0;
            }
        } catch(NullPointerException e) {
        }
        //For parabola()
        Vi = 0;
        Vx = 0;
        Vy = 0;
        T_max = 0;
        Y_displ = 0;
        X_displ = 0;
        h = 0;
        k = 0;
        a_parab = 0;
    }

    public void clear() {
        display.setText("");
        stor = "";
        typeDot = true;
        initial = true;
    }

    public static void main(String[] arguments) {
        CalcClass c = new CalcClass();
    }
}

Ok so now you've seen my mess... I sort-of know what I should do and YES I did some research but I feel it would be much easier to learn organization through example or a nice push than it would be from reading articles that tell you ultra-hypothetical or loosely-analogous examples of what objects are. Note: I tried using methods to organize and my class looks much better than what it did (I also made the whole thing an object to be called upon at the bottom which is pretty much useless).

Answer 1

If you use eclipse, try:

Window > Prefferences > Java > Editor > Save Actions

Check "perform the selected actions on save", "Additional Actions" and click "Configure".

Using eclipse's Save Actions can be really useful in real life coding, but you will probably learn some neat java tricks going through the Save Actions wizard.

Java is an Object Oriented language. You need to take advantage of that fact.
Use classes to separate your code into different logical / structural components. Learn how to use OOP. Follow SOLID design and use design patterns .

Another important thing is to know your language . Start by reading basic classes javadoc s and relevant sections of the java spec. I would begin with deeply understanding the different types of java ( class , interface , enum and inner / nested / anonymous types) and the different modifiers ( private , public , protected , static , abstract , final , default ).

Some other eclipse's short cuts:

CTRL-A , CTRL-I ("indentation") will fix your code indentation.

CTRL-SHIFT-O ("organize imports") will omit redundant imports.

Answer 2

You might consider taking a look at Code Complete, which deals with the issues that you're concerned with here, and otherwise is just a classic in our field that every serious developer should read.

In general, when you're organizing code you should do so with a few things in mind: readability and atomicity. These two factors apply to code on every level of an application, from variable naming, routines, methods, classes, packages, and so on.

Readability is a simple idea: can a human being read this code and understand it? To gauge the readability of the code all you have to do is read it! Do variable names help the reader understand what something is? Are routines and classes properly formatted and not needlessly complex? Have you removed all code that isn't being used? Is your code written in a logical progression?

Atomicity is the idea that everything should have one purpose. A function or method should (usually) do one thing and one thing only. A class should usually be a logical grouping of related methods and fields serving some type of unique purpose, and NOT a mish-mash of unrelated stuff. A package should also contain a set of related files. Same with a project, and so on.

The main benefit of atomicity is that once you get into more involved applications it's actually much easier to debug and isolate issues in your code because you know where stuff is . For instance: I have a database access error! Good thing I have a package that's specifically defined for my database access objects.

I know when I was just getting started in the field this was something that threw me off too. It might not be until you do a lot of coding within more significant apps that you really start to understand best practices and why people build stuff a certain way.

Answer 3

Thanks to everyone who contributed to my problem, I completely scrapped this garbage and made it 1000 times better. I knew from the beginning it was poorly made and I wanted to fix it, I just didn't know where to start. After reading all the advice that was given, watching a few tutorials and brushing up on some simple java concepts (modifiers, jswing, etc), I ended up making a new one that is in MVC format (Yay, order and efficiency). Now all my new variables are actually meaningful (Thanks @maaartinus for helping me realize that many of my variables were poorly named and made my whole program unnecessarily complicated). Also, I tried to work on SRP (Not 100% sure if I completely did it but with the program organized it will be easy to change things) and I plan on adding units later for good practice (Thank you, @Robert Snyder). This new GUI is ugly but that can always be changed later and since It is now in MVC format the job will be easier.

Here is what I did (not finished and far from perfect but a step in the right direction):

CalcGui.java

package com.Calculator;

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class CalcGui extends JFrame {

private static final long serialVersionUID = 1L;
private String[] operatorsList = { "+", "-", "*", "/", "^" };

// Row 1
private JTextField firstNumber = new JTextField(10);
private JComboBox<String> operator = new JComboBox<>(operatorsList);
private JTextField secondNumber = new JTextField(10);
private JButton calculateButton = new JButton("Calculate");
private JTextField calcSolution = new JTextField(20);

// Row 2
private JLabel sqrtSymbol = new JLabel("√");
private JTextField sqrtNumber = new JTextField(10);
private JButton sqrtCalcButton = new JButton("Calculate");
private JTextField sqrtCalcSolution = new JTextField(20);

// Row 3
private JLabel quadraticLabel1 = new JLabel("A = ");
private JTextField quadraticFirstNumber = new JTextField(5);
private JLabel quadraticLabel2 = new JLabel("B = ");
private JTextField quadraticSecondNumber = new JTextField(5);
private JLabel quadraticLabel3 = new JLabel("C = ");
private JTextField quadraticThirdNumber = new JTextField(5);
private JButton quadraticCalcButton = new JButton("Calculate");
private JLabel quadraticTextBefore = new JLabel("x =");
private JTextField firstQuadraticCalcSolution = new JTextField(3);
private JLabel quadraticTextMiddle = new JLabel("and x =");
private JTextField secondQuadraticCalcSolution = new JTextField(3);

CalcGui() {

    JPanel calcPanel = new JPanel(new BorderLayout());
    FlowLayout Default = new FlowLayout(FlowLayout.LEFT);
    JPanel row1 = new JPanel(Default);
    JPanel row2 = new JPanel(Default);
    JPanel row3 = new JPanel(Default);

    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.setSize(650, 150);

    row1.add(firstNumber);
    row1.add(operator);
    row1.add(secondNumber);
    row1.add(calculateButton);
    row1.add(calcSolution);

    row2.add(sqrtSymbol);
    row2.add(sqrtNumber);
    row2.add(sqrtCalcButton);
    row2.add(sqrtCalcSolution);

    row3.add(quadraticLabel1);
    row3.add(quadraticFirstNumber);
    row3.add(quadraticLabel2);
    row3.add(quadraticSecondNumber);
    row3.add(quadraticLabel3);
    row3.add(quadraticThirdNumber);
    row3.add(quadraticCalcButton);
    row3.add(quadraticTextBefore);
    row3.add(firstQuadraticCalcSolution);
    row3.add(quadraticTextMiddle);
    row3.add(secondQuadraticCalcSolution);

    calcPanel.add(row1, BorderLayout.NORTH);
    calcPanel.add(row2, BorderLayout.CENTER);
    calcPanel.add(row3, BorderLayout.SOUTH);
    this.add(calcPanel);

}

// basic calculations methods
public double getFirstNumber() {

    return Double.parseDouble(firstNumber.getText());

}

public String getOperator() {

    return (String) operator.getSelectedItem();

}

public double getSecondNumber() {

    return Double.parseDouble(secondNumber.getText());

}

public void setCalcSolution(double solution) {

    calcSolution.setText(Double.toString(solution));

}

void addCalculateListener(ActionListener listenForCalcButton) {

    calculateButton.addActionListener(listenForCalcButton);

}

void displayErrorMessage(String errorMessage) {

    JOptionPane.showMessageDialog(this, errorMessage);

}

// Square root function methods
public double getSqrtNumber() {

    return Double.parseDouble(sqrtNumber.getText());

}

public void setSqrtCalcSolution(double solution) {

    sqrtCalcSolution.setText(Double.toString(solution));

}

void addSqrtCalcListener(ActionListener listenForSqrtCalcButton) {

    sqrtCalcButton.addActionListener(listenForSqrtCalcButton);

}

// Quadratic formula Methods
public double getQuadraticFirstNumber() {

    return Double.parseDouble(quadraticFirstNumber.getText());

}

public double getQuadraticSecondNumber() {

    return Double.parseDouble(quadraticSecondNumber.getText());

}

public double getQuadraticThirdNumber() {

    return Double.parseDouble(quadraticThirdNumber.getText());

}

public void setFirstQuadraticCalcSolution(double solution) {

    firstQuadraticCalcSolution.setText(Double.toString(solution));

}

public void setSecondQuadraticCalcSolution(double solution) {

    secondQuadraticCalcSolution.setText(Double.toString(solution));

}

void addQuadraticCalcListener(ActionListener listenForQuadraticCalcButton) {

    quadraticCalcButton.addActionListener(listenForQuadraticCalcButton);

}
}

CalcModel.java

package com.Calculator;

public class CalcModel {

private double calcValue;

public void calculate(double firstNumber, double secondNumber,
        String operator) {

    if (operator.equals("+")) {

        calcValue = firstNumber + secondNumber;

    }

    if (operator.equals("-")) {

        calcValue = firstNumber - secondNumber;

    }
    if (operator.equals("*")) {

        calcValue = firstNumber * secondNumber;

    }
    if (operator.equals("/")) {

        calcValue = firstNumber / secondNumber;

    }

    if (operator.equals("^")) {

        calcValue = Math.pow(firstNumber, secondNumber);

    }
}

public double getCalcValue() {

    return calcValue;

}

}

SqrtCalcModel.java

package com.Calculator;

public class SqrtCalcModel {

private double sqrtCalcValue;

public void sqrt(double number) {

    sqrtCalcValue = Math.sqrt(number);

}

public double getSqrtCalcValue() {

    return sqrtCalcValue;

}
}

QuadraticCalcModel.java

package com.Calculator;

import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class QuadraticCalcModel {

private double firstQuadraticCalcValue;
private double secondQuadraticCalcValue;

public void quadraticFormula(double a, double b, double c) {

    double discriminant = (b * b) - (4 * a * c);

    if (discriminant >= 0) {

        firstQuadraticCalcValue = (Math.sqrt((b * b) - (4 * a * c)) + (-b))
                / (2 * a);

        secondQuadraticCalcValue = (Math.sqrt((b * b) - (4 * a * c)) - (-b))
                / (2 * a);

    }

    else {

        JFrame parent = new JFrame();
        JOptionPane.showMessageDialog(parent,
                "This function has no real roots.");

    }

}

public double getFirstQuadraticValue() {

    return firstQuadraticCalcValue;

}

public double getSecondQuadraticValue() {

    return secondQuadraticCalcValue;

}

}

CalculatorControler.java

package com.Calculator;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class CalculatorController {

private CalcGui theGui;
private CalcModel theCalcModel;
private SqrtCalcModel theSqrtCalcModel;
private QuadraticCalcModel theQuadraticCalcModel;

public CalculatorController(CalcGui theGui, CalcModel theCalcModel,
        SqrtCalcModel theSqrtCalcModel,
        QuadraticCalcModel theQuadraticCalcModel) {
    this.theGui = theGui;
    this.theCalcModel = theCalcModel;
    this.theSqrtCalcModel = theSqrtCalcModel;
    this.theQuadraticCalcModel = theQuadraticCalcModel;

    this.theGui.addCalculateListener(new CalcListener());
    this.theGui.addSqrtCalcListener(new SqrtCalcListener());
    this.theGui.addQuadraticCalcListener(new QuadraticCalcListener());
}

class CalcListener implements ActionListener {

    public void actionPerformed(ActionEvent e) {

        double firstNumber, secondNumber = 0;
        String operator;

        try {

            firstNumber = theGui.getFirstNumber();
            operator = theGui.getOperator();
            secondNumber = theGui.getSecondNumber();

            theCalcModel.calculate(firstNumber, secondNumber, operator);

            theGui.setCalcSolution(theCalcModel.getCalcValue());

        }

        catch (NumberFormatException ex) {

            System.out.println(ex);

            theGui.displayErrorMessage("You Need to Enter 2 Numbers");

        }
    }
}

class SqrtCalcListener implements ActionListener {

    public void actionPerformed(ActionEvent e) {

        double number = 0;

        try {

            number = theGui.getSqrtNumber();

            theSqrtCalcModel.sqrt(number);

            theGui.setSqrtCalcSolution(theSqrtCalcModel.getSqrtCalcValue());

        }

        catch (NumberFormatException ex) {
            System.out.println(ex);

            theGui.displayErrorMessage("You Need to enter a Number");
        }
    }
}

class QuadraticCalcListener implements ActionListener {

    public void actionPerformed(ActionEvent e) {

        double a, b, c = 0;

        try {

            a = theGui.getQuadraticFirstNumber();
            b = theGui.getQuadraticSecondNumber();
            c = theGui.getQuadraticThirdNumber();

            theQuadraticCalcModel.quadraticFormula(a, b, c);

            theGui.setFirstQuadraticCalcSolution(theQuadraticCalcModel
                    .getFirstQuadraticValue());

            theGui.setSecondQuadraticCalcSolution(theQuadraticCalcModel
                    .getSecondQuadraticValue());

        }

        catch (NumberFormatException ex) {

            System.out.println(ex);

            theGui.displayErrorMessage("You need to enter 3 numbers.");
        }

    }
}

}

MVCCalculator.java

package com.Calculator;

public class MVCCalculator {

public static void main(String[] args) {

    CalcGui theGui = new CalcGui();

    CalcModel theCalcModel = new CalcModel();

    SqrtCalcModel theSqrtCalcModel = new SqrtCalcModel();

    QuadraticCalcModel theQuadraticCalcModel = new QuadraticCalcModel();

    new CalculatorController(theGui, theCalcModel, theSqrtCalcModel,
            theQuadraticCalcModel);

    theGui.setVisible(true);

}
}