In this tutorial, we will develop a simple Calculator project using Java Swing.
We also write a JUnit test to test Calculator implementation logic.
Requirements
- Java 8+
- IDE - Eclipse or IntelliJ IDEA
- JUnit 5 Framework
1. Create a Simple Maven Java Project
Let's give the project name as Calculator and add below JUnit 5 dependency:
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>5.7.0</version>
<scope>test</scope>
</dependency>2. Calculator Implementation using Java Swing
Let's create a Java class named Calculator and add the following content to it:
import java.awt.Cursor;
import java.awt.Font;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.util.function.Consumer;
import java.util.regex.Pattern;
import java.awt.Color;
import javax.swing.*;
import java.lang.Math;
public class Calculator {
private static final int WINDOW_WIDTH = 410;
private static final int WINDOW_HEIGHT = 600;
private static final int BUTTON_WIDTH = 80;
private static final int BUTTON_HEIGHT = 70;
private static final int MARGIN_X = 20;
private static final int MARGIN_Y = 60;
private JFrame window; // Main window
private JComboBox<String> comboCalcType, comboTheme;
private JTextField inText; // Input
private JButton btnC, btnBack, btnMod, btnDiv, btnMul, btnSub, btnAdd,
btn0, btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9,
btnPoint, btnEqual, btnRoot, btnPower, btnLog;
private char opt = ' '; // Save the operator
private boolean go = true; // For calculate with Opt != (=)
private boolean addWrite = true; // Connect numbers in display
private double val = 0; // Save the value typed for calculation
/*
Mx Calculator:
X = Row
Y = Column
+-------------------+
| +-----------+ | y[0]
| | | |
| +-----------+ |
| |
| C <- % / | y[1]
| 7 8 9 * | y[2]
| 4 5 6 - | y[3]
| 1 2 3 + | y[4]
| . 0 = | y[5]
+-------------------+
x[0] x[1] x[2] x[3]
*/
/*
+-------------------+
| +-----------+ | y[0]
| | | |
| +-----------+ |
| |
| 0 1 1 3 | y[1]
| 4 5 6 7 | y[2]
| 8 9 10 11 | y[3]
| 12 13 14 15 | y[4]
| 16 17 18 | y[5]
+-------------------+
x[0] x[1] x[2] x[3]
*/
public Calculator() {
window = new JFrame("Calculator");
window.setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
window.setLocationRelativeTo(null); // Move window to center
comboTheme = initCombo(new String[]{"Simple", "Colored", "DarkTheme"}, 230, 30, "Theme", themeSwitchEventConsumer);
comboCalcType = initCombo(new String[]{"Standard", "Scientific"}, 20, 30, "Calculator type", calcTypeSwitchEventConsumer);
int[] x = {MARGIN_X, MARGIN_X + 90, 200, 290, 380};
int[] y = {MARGIN_Y, MARGIN_Y + 100, MARGIN_Y + 180, MARGIN_Y + 260, MARGIN_Y + 340, MARGIN_Y + 420};
inText = new JTextField("0");
inText.setBounds(x[0], y[0], 350, 70);
inText.setEditable(false);
inText.setBackground(Color.WHITE);
inText.setFont(new Font("Comic Sans MS", Font.PLAIN, 33));
window.add(inText);
btnC = initBtn("C", x[0], y[1], event -> {
repaintFont();
inText.setText("0");
opt = ' ';
val = 0;
});
btnBack = initBtn("<-", x[1], y[1], event -> {
repaintFont();
String str = inText.getText();
StringBuilder str2 = new StringBuilder();
for (int i = 0; i < (str.length() - 1); i++) {
str2.append(str.charAt(i));
}
if (str2.toString().equals("")) {
inText.setText("0");
} else {
inText.setText(str2.toString());
}
});
btnMod = initBtn("%", x[2], y[1], event -> {
repaintFont();
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = calc(val, inText.getText(), opt);
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = '%';
go = false;
addWrite = false;
}
});
btnDiv = initBtn("/", x[3], y[1], event -> {
repaintFont();
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = calc(val, inText.getText(), opt);
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = '/';
go = false;
addWrite = false;
} else {
opt = '/';
}
});
btn7 = initBtn("7", x[0], y[2], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("7");
} else {
inText.setText(inText.getText() + "7");
}
} else {
inText.setText("7");
addWrite = true;
}
go = true;
});
btn8 = initBtn("8", x[1], y[2], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("8");
} else {
inText.setText(inText.getText() + "8");
}
} else {
inText.setText("8");
addWrite = true;
}
go = true;
});
btn9 = initBtn("9", x[2], y[2], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("9");
} else {
inText.setText(inText.getText() + "9");
}
} else {
inText.setText("9");
addWrite = true;
}
go = true;
});
btnMul = initBtn("*", x[3], y[2], event -> {
repaintFont();
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = calc(val, inText.getText(), opt);
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = '*';
go = false;
addWrite = false;
} else {
opt = '*';
}
});
btn4 = initBtn("4", x[0], y[3], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("4");
} else {
inText.setText(inText.getText() + "4");
}
} else {
inText.setText("4");
addWrite = true;
}
go = true;
});
btn5 = initBtn("5", x[1], y[3], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("5");
} else {
inText.setText(inText.getText() + "5");
}
} else {
inText.setText("5");
addWrite = true;
}
go = true;
});
btn6 = initBtn("6", x[2], y[3], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("6");
} else {
inText.setText(inText.getText() + "6");
}
} else {
inText.setText("6");
addWrite = true;
}
go = true;
});
btnSub = initBtn("-", x[3], y[3], event -> {
repaintFont();
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = calc(val, inText.getText(), opt);
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = '-';
go = false;
addWrite = false;
} else {
opt = '-';
}
});
btn1 = initBtn("1", x[0], y[4], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("1");
} else {
inText.setText(inText.getText() + "1");
}
} else {
inText.setText("1");
addWrite = true;
}
go = true;
});
btn2 = initBtn("2", x[1], y[4], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("2");
} else {
inText.setText(inText.getText() + "2");
}
} else {
inText.setText("2");
addWrite = true;
}
go = true;
});
btn3 = initBtn("3", x[2], y[4], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("3");
} else {
inText.setText(inText.getText() + "3");
}
} else {
inText.setText("3");
addWrite = true;
}
go = true;
});
btnAdd = initBtn("+", x[3], y[4], event -> {
repaintFont();
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = calc(val, inText.getText(), opt);
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = '+';
go = false;
addWrite = false;
} else {
opt = '+';
}
});
btnPoint = initBtn(".", x[0], y[5], event -> {
repaintFont();
if (addWrite) {
if (!inText.getText().contains(".")) {
inText.setText(inText.getText() + ".");
}
} else {
inText.setText("0.");
addWrite = true;
}
go = true;
});
btn0 = initBtn("0", x[1], y[5], event -> {
repaintFont();
if (addWrite) {
if (Pattern.matches("[0]*", inText.getText())) {
inText.setText("0");
} else {
inText.setText(inText.getText() + "0");
}
} else {
inText.setText("0");
addWrite = true;
}
go = true;
});
btnEqual = initBtn("=", x[2], y[5], event -> {
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = calc(val, inText.getText(), opt);
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = '=';
addWrite = false;
}
});
btnEqual.setSize(2 * BUTTON_WIDTH + 10, BUTTON_HEIGHT);
btnRoot = initBtn("√", x[4], y[1], event -> {
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = Math.sqrt(Double.parseDouble(inText.getText()));
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = '√';
addWrite = false;
}
});
btnRoot.setVisible(false);
btnPower = initBtn("pow", x[4], y[2], event -> {
repaintFont();
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = calc(val, inText.getText(), opt);
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = '^';
go = false;
addWrite = false;
} else {
opt = '^';
}
});
btnPower.setFont(new Font("Comic Sans MS", Font.PLAIN, 24));
btnPower.setVisible(false);
btnLog = initBtn("ln", x[4], y[3], event -> {
if (Pattern.matches("([-]?\\d+[.]\\d*)|(\\d+)", inText.getText()))
if (go) {
val = Math.log(Double.parseDouble(inText.getText()));
if (Pattern.matches("[-]?[\\d]+[.][0]*", String.valueOf(val))) {
inText.setText(String.valueOf((int) val));
} else {
inText.setText(String.valueOf(val));
}
opt = 'l';
addWrite = false;
}
});
btnLog.setVisible(false);
window.setLayout(null);
window.setResizable(false);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // Close button clicked? = End The process
window.setVisible(true);
}
private JComboBox<String> initCombo(String[] items, int x, int y, String toolTip, Consumer consumerEvent) {
JComboBox<String> combo = new JComboBox<>(items);
combo.setBounds(x, y, 140, 25);
combo.setToolTipText(toolTip);
combo.setCursor(new Cursor(Cursor.HAND_CURSOR));
combo.addItemListener(consumerEvent::accept);
window.add(combo);
return combo;
}
private JButton initBtn(String label, int x, int y, ActionListener event) {
JButton btn = new JButton(label);
btn.setBounds(x, y, BUTTON_WIDTH, BUTTON_HEIGHT);
btn.setFont(new Font("Comic Sans MS", Font.PLAIN, 28));
btn.setCursor(new Cursor(Cursor.HAND_CURSOR));
btn.addActionListener(event);
btn.setFocusable(false);
window.add(btn);
return btn;
}
public double calc(double x, String input, char opt) {
inText.setFont(inText.getFont().deriveFont(Font.PLAIN));
double y = Double.parseDouble(input);
switch (opt) {
case '+':
return x + y;
case '-':
return x - y;
case '*':
return x * y;
case '/':
return x / y;
case '%':
return x % y;
case '^':
return Math.pow(x, y);
default:
inText.setFont(inText.getFont().deriveFont(Font.PLAIN));
return y;
}
}
private void repaintFont() {
inText.setFont(inText.getFont().deriveFont(Font.PLAIN));
}
private Consumer<ItemEvent> calcTypeSwitchEventConsumer = event -> {
if (event.getStateChange() != ItemEvent.SELECTED) return;
String selectedItem = (String) event.getItem();
switch (selectedItem) {
case "Standard":
window.setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
btnRoot.setVisible(false);
btnPower.setVisible(false);
btnLog.setVisible(false);
break;
case "Scientific":
window.setSize(WINDOW_WIDTH + 80, WINDOW_HEIGHT);
btnRoot.setVisible(true);
btnPower.setVisible(true);
btnLog.setVisible(true);
break;
}
};
private Consumer<ItemEvent> themeSwitchEventConsumer = event -> {
if (event.getStateChange() != ItemEvent.SELECTED) return;
String selectedTheme = (String) event.getItem();
switch (selectedTheme) {
case "Simple":
window.getContentPane().setBackground(null);
btnC.setBackground(null);
btnBack.setBackground(null);
btnMod.setBackground(null);
btnDiv.setBackground(null);
btnMul.setBackground(null);
btnSub.setBackground(null);
btnAdd.setBackground(null);
btnRoot.setBackground(null);
btnLog.setBackground(null);
btnPower.setBackground(null);
btnEqual.setBackground(null);
btn0.setBackground(null);
btn1.setBackground(null);
btn2.setBackground(null);
btn3.setBackground(null);
btn4.setBackground(null);
btn5.setBackground(null);
btn6.setBackground(null);
btn7.setBackground(null);
btn8.setBackground(null);
btn9.setBackground(null);
btnPoint.setBackground(null);
btnC.setForeground(Color.BLACK);
btnBack.setForeground(Color.BLACK);
btnMod.setForeground(Color.BLACK);
btnDiv.setForeground(Color.BLACK);
btnMul.setForeground(Color.BLACK);
btnSub.setForeground(Color.BLACK);
btnAdd.setForeground(Color.BLACK);
btnEqual.setForeground(Color.BLACK);
btnLog.setForeground(Color.BLACK);
btnPower.setForeground(Color.BLACK);
btnRoot.setForeground(Color.BLACK);
break;
case "Colored":
window.getContentPane().setBackground(null);
btnC.setBackground(Color.RED);
btnBack.setBackground(Color.ORANGE);
btnMod.setBackground(Color.GREEN);
btnDiv.setBackground(Color.PINK);
btnMul.setBackground(Color.PINK);
btnSub.setBackground(Color.PINK);
btnAdd.setBackground(Color.PINK);
btnRoot.setBackground(Color.PINK);
btnLog.setBackground(Color.PINK);
btnPower.setBackground(Color.PINK);
btnEqual.setBackground(Color.BLUE);
btn0.setBackground(Color.WHITE);
btn1.setBackground(Color.WHITE);
btn2.setBackground(Color.WHITE);
btn3.setBackground(Color.WHITE);
btn4.setBackground(Color.WHITE);
btn5.setBackground(Color.WHITE);
btn6.setBackground(Color.WHITE);
btn7.setBackground(Color.WHITE);
btn8.setBackground(Color.WHITE);
btn9.setBackground(Color.WHITE);
btnPoint.setBackground(Color.WHITE);
btnC.setForeground(Color.WHITE);
btnBack.setForeground(Color.WHITE);
btnMod.setForeground(Color.WHITE);
btnDiv.setForeground(Color.WHITE);
btnMul.setForeground(Color.WHITE);
btnSub.setForeground(Color.WHITE);
btnAdd.setForeground(Color.WHITE);
btnEqual.setForeground(Color.WHITE);
btnLog.setForeground(Color.WHITE);
btnPower.setForeground(Color.WHITE);
btnRoot.setForeground(Color.WHITE);
break;
case "DarkTheme":
final Color primaryDarkColor = new Color(141, 38, 99);
final Color secondaryDarkColor = new Color(171, 171, 171);
window.getContentPane().setBackground(new Color(68, 68, 68));
btn0.setBackground(secondaryDarkColor);
btn1.setBackground(secondaryDarkColor);
btn2.setBackground(secondaryDarkColor);
btn3.setBackground(secondaryDarkColor);
btn4.setBackground(secondaryDarkColor);
btn5.setBackground(secondaryDarkColor);
btn6.setBackground(secondaryDarkColor);
btn7.setBackground(secondaryDarkColor);
btn8.setBackground(secondaryDarkColor);
btn9.setBackground(secondaryDarkColor);
btnPoint.setBackground(secondaryDarkColor);
btnC.setForeground(secondaryDarkColor);
btnBack.setForeground(secondaryDarkColor);
btnMod.setForeground(secondaryDarkColor);
btnDiv.setForeground(secondaryDarkColor);
btnMul.setForeground(secondaryDarkColor);
btnSub.setForeground(secondaryDarkColor);
btnAdd.setForeground(secondaryDarkColor);
btnEqual.setForeground(secondaryDarkColor);
btnLog.setForeground(secondaryDarkColor);
btnPower.setForeground(secondaryDarkColor);
btnRoot.setForeground(secondaryDarkColor);
btnC.setBackground(primaryDarkColor);
btnBack.setBackground(primaryDarkColor);
btnMod.setBackground(primaryDarkColor);
btnDiv.setBackground(primaryDarkColor);
btnMul.setBackground(primaryDarkColor);
btnSub.setBackground(primaryDarkColor);
btnAdd.setBackground(primaryDarkColor);
btnRoot.setBackground(primaryDarkColor);
btnLog.setBackground(primaryDarkColor);
btnPower.setBackground(primaryDarkColor);
btnEqual.setBackground(primaryDarkColor);
}
};
public static void main(String[] args) {
new Calculator();
}
}This Calculator class has a main() method so simply run this class to open the Calculator in Window.
Demo
Simple:
Colored:
JUnit Test to test Calculator Logic
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
class CalculatorTest {
private Calculator calculator;
@BeforeEach
void setUp() { // Create object before compilation
calculator = new Calculator();
}
/*
* testCalc() test method
*/
@Test
void testCalc() {
double first = 3;
String second = "5";
try {
Assertions.assertEquals(8, calculator.calc(first, second, '+'));
Assertions.assertEquals(-2, calculator.calc(first, second, '-'));
Assertions.assertEquals(15, calculator.calc(first, second, '*'));
Assertions.assertEquals(0.6, calculator.calc(first, second, '/'));
Assertions.assertEquals(3d, calculator.calc(first, second, '%'));
Assertions.assertEquals(243, calculator.calc(first, second, '^'));
} catch (Exception e) {
e.printStackTrace();
}
}
}
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