1. The calculator – Java GUI
Lesson 30:
The calculator – Java GUI

2. Many Buttons RECAP // Addition.java import java.awt.event.*;
class Addition implements ActionListener{
public void actionPerformed(ActionEvent e) {
System.out.println("The answer is 4");
System.exit(0); }
// Subtraction.java
class Subtraction implements ActionListener{
System.out.println("The answer is 111");
// GoodBye.java
class GoodBye implements ActionListener{
System.out.println("Goodbye!");
RECAP
Many Buttons

3. Text input // TextInput.java import java.awt.*; import javax.swing.*;
RECAP
// TextInput.java
import java.awt.*;
import javax.swing.*;
class TextInput {
public static void main (String[] args){
JFrame frame = new JFrame("textInput");
Container pane = frame.getContentPane();
JTextField input = new JTextField("enter text and press return");
Echo listner=new Echo();
input.addActionListener(listener);
pane.add(input);
frame.pack();
frame.show(); }

4. Text input // Echo.java import java.awt.event.*;
RECAP
// Echo.java
import java.awt.event.*;
class Echo implements ActionListener{
public void actionPerformed(ActionEvent e) {
JTextField source =(JTextField)e.getSource();
String text = source.getText();
System.out.println("text");
System.exit(0); }

5. The Calculator In this example we will start using
JLabels
the GridLayout
Typecasting to double from a text input
With use of JButtons, JFrame, Containers, Listeners and JTextFields we will create a calculator java application using the GUI components in the swing library

6. The Calculator

7. Imporing the libraries
// MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
Imporing the libraries
Creating the MiniCalc class
The main section of the program

8. Creating a frame called frame and labeled MiniCalc
// MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
Creating a frame called frame and labeled MiniCalc
Creating a container for the frame
Creating text field based on the JTextField provided by the library
The length of the field
The name of the field

9. // MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
Creating 3 text fields
Creating a button named addButton based on the JButton and labeled “Add”
Creating a button named subButton based on the JButton and labeled “Subtract”

10. Dividing the Container in a grid with 4 rows and 2 columns
// MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
Dividing the Container in a grid with 4 rows and 2 columns

11. Adding a label “enter a number” to the pane container
// MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
Adding a label “enter a number” to the pane container
Adding a the textfield firstNumber to the pane container

12. Adding all labels, text fields and buttons to the container
// MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
Adding all labels, text fields and buttons to the container

13. Assigning the listener to each of the buttons
// MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
Creating a listener based on the DoMath class (we will look at this in a little while)
Assigning the listener to each of the buttons

14. Shrink the frame to minimal size
// MiniCalc.java - demo gridlayout
import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
Determins the width of the column, and therefore the size of th frame and buttons (we are using the pack method
Shrink the frame to minimal size
Show the frame with the content in the container

15. Importing the awt.event package from the library that contains the various event listing interfaces.
// DoMath.java
import javax.swing.*;
import java.awt.event.*;
class DoMath implements ActionListener{
DoMath(JTextField first, JTextField second, JTextField result){
inputOne = first;
inputTwo = second;
output = result; }
public void actionPerformed(ActionEvent e){
double first, second;
first = Double.parseDouble(inputOne.getText().trim());
second = Double.parseDouble(inputTwo.getText().trim());
if (e.getActionCommand().equals("Add"))
output.setText(String.valueOf(first+second));
else
output.setText(String.valueOf(first-second));
private JTextField inputOne, inputTwo, output;
This example use the interface ActionListener to indicate that DoMath contains the method actionPerformed().

16. These are private variables defined in this class
Here we indicate that the class DoMath contains all methods specified in the interface ActionListener. That is to say that the class implements the interface ActionListener
// DoMath.java
import javax.swing.*;
import java.awt.event.*;
class DoMath implements ActionListener{
DoMath(JTextField first, JTextField second, JTextField result){
inputOne = first;
inputTwo = second;
output = result; }
public void actionPerformed(ActionEvent e){
double first, second;
first = Double.parseDouble(inputOne.getText().trim());
second = Double.parseDouble(inputTwo.getText().trim());
if (e.getActionCommand().equals("Add"))
output.setText(String.valueOf(first+second));
else
output.setText(String.valueOf(first-second));
private JTextField inputOne, inputTwo, output;
The DoMath method is defined as accepting 3 JTextFields that are translated into 3 fields called inputOne, inputTwo and output.
These are private variables defined in this class

17. Creating to primitive double variables
This method is called when the button is clicked. It is executed through the actionPerformed method, which , as we covered before, for a JButton is a mouseclick.
// DoMath.java
import javax.swing.*;
import java.awt.event.*;
class DoMath implements ActionListener{
DoMath(JTextField first, JTextField second, JTextField result){
inputOne = first;
inputTwo = second;
output = result; }
public void actionPerformed(ActionEvent e){
double first, second;
first = Double.parseDouble(inputOne.getText().trim());
second = Double.parseDouble(inputTwo.getText().trim());
if (e.getActionCommand().equals("Add"))
output.setText(String.valueOf(first+second));
else
output.setText(String.valueOf(first-second));
private JTextField inputOne, inputTwo, output;
Creating to primitive double variables
Gets the string text
Removing any spaces
Converting a string to a double

18. // DoMath.java
import javax.swing.*;
import java.awt.event.*;
class DoMath implements ActionListener{
DoMath(JTextField first, JTextField second, JTextField result){
inputOne = first;
inputTwo = second;
output = result; }
public void actionPerformed(ActionEvent e){
double first, second;
first = Double.parseDouble(inputOne.getText().trim());
second = Double.parseDouble(inputTwo.getText().trim());
if (e.getActionCommand().equals("Add"))
output.setText(String.valueOf(first+second));
else
output.setText(String.valueOf(first-second));
private JTextField inputOne, inputTwo, output;
This returns the actionCommand string associated with the button. By default this is the label of the button
If the button clicked is the button labeled “Add” we will set the output variable to the string text of the valueOf (first+second)

19. Simple if…else statement
// DoMath.java
import javax.swing.*;
import java.awt.event.*;
class DoMath implements ActionListener{
DoMath(JTextField first, JTextField second, JTextField result){
inputOne = first;
inputTwo = second;
output = result; }
public void actionPerformed(ActionEvent e){
double first, second;
first = Double.parseDouble(inputOne.getText().trim());
second = Double.parseDouble(inputTwo.getText().trim());
if (e.getActionCommand().equals("Add"))
output.setText(String.valueOf(first+second));
else
output.setText(String.valueOf(first-second));
private JTextField inputOne, inputTwo, output;
Simple if…else statement

20. Compiling the files

21. Running the application