Develop Reference

Issues Getting Button to Change Label Text

Recently I've been trying to make a program that takes in a double in the form of a string. It then parses that to a double which goes to another class to be divided to a quarter or a half and then returns that output to a label.
I've been having an issue where when I click a button to actually submit what is inside the text field, the label doesn't change.
I've tried a lot of trial and error and I know I can change the text after doing new JLabel("test") for example. However, there seems to be an issue with my action listener for when the button is pushed. I can't tell if it's not seeing the button as being pushed.
NOTE: I am new to awt event things and swing as a whole, I usually operate just using the output terminal of visual studio code where it's just text and no graphics.
import javax.swing.*;
import java.awt.event.*;
import java.awt.Font;
import java.awt.Dimension;
public class MoneySorterRunner {
private MoneySorter sorter = new MoneySorter();
private String input = "0";
private double money = Double.parseDouble(input);
private static JTextField typeHere = new JTextField();
///labels num1-3 are the labels being changed
private static JLabel num1 = new JLabel(new MoneySorterRunner().sorter.divQuarter(new MoneySorterRunner().money));
private static JLabel num2 = new JLabel(new MoneySorterRunner().sorter.divQuarter(new MoneySorterRunner().money));
private static JLabel num3 = new JLabel(new MoneySorterRunner().sorter.divHalf(new MoneySorterRunner().money));
public static void main(String args[]) {
JFrame frame = new JFrame("Money Calculator - v0.1a");
JPanel panel = new JPanel();
JButton doThing = new JButton("Do a Thing");
doThing.setActionCommand("Do a Thing");
frame.add(panel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500, 250);
frame.setLocation(200, 200);
frame.setResizable(false);
frame.setLocationRelativeTo(null);
panel.setLayout(null);
frame.setVisible(true);
JLabel item1 = new JLabel("test");
JLabel item2 = new JLabel("test");
JLabel item3 = new JLabel("test");
item1.setFont(new Font("Arial", Font.PLAIN, 30));
item2.setFont(new Font("Arial", Font.PLAIN, 30));
item3.setFont(new Font("Arial", Font.PLAIN, 30));
num1.setFont(new Font("Arial", Font.PLAIN, 25));
num2.setFont(new Font("Arial", Font.PLAIN, 25));
num3.setFont(new Font("Arial", Font.PLAIN, 25));
Dimension size1 = item1.getPreferredSize();
Dimension size2 = item2.getPreferredSize();
Dimension size3 = item3.getPreferredSize();
panel.add(item1);
panel.add(item2);
panel.add(item3);
panel.add(num1);
panel.add(num2);
panel.add(num3);
panel.add(doThing);
panel.add(typeHere);
item1.setBounds(10, 10, size1.width + 3, size1.height);
item2.setBounds(190, 10, size2.width + 3, size2.height);
item3.setBounds(325, 10, size3.width + 3, size3.height);
num1.setBounds(50, 50, 50, 25);
num2.setBounds(200, 50, 50, 25);
num3.setBounds(350, 50, 50, 25);
doThing.setBounds(250, 150, 100, 25);
typeHere.setBounds(100, 150, 150, 25);
}
public void actionPerformed(ActionEvent event){
String check = event.getActionCommand();
if(check.equals("Do a Thing")){
input = typeHere.getText();
}
if(input != "0"){
num1.setText(sorter.divQuarter(money));
num2.setText(sorter.divQuarter(money));
num3.setText(sorter.divHalf(money));
}
}
}
For those who wanted the MoneySorter.java:
public MoneySorter(){
}
public String divQuarter(double moneyIn){
String answer = Double.toString(moneyIn);
return answer;
}
public String divHalf(double moneyIn){
String answer = Double.toString(moneyIn);
return answer;
}
}

I understand that your program is supposed to do the following.
User enters an amount of money in a JTextField and when she clicks on a JButton the JLabels show the entered amount in dollars, half-dollars and quarters (as per U.S. currency). My answer, below, is based on this understanding.
I don't know if making all the variables static is good or bad but I never use static class member variables in my Swing programs.
Here is my analysis of your code.
private double money = Double.parseDouble(input);
This line of code will be executed precisely once, when you launch class MoneySorterRunner. You want to do this every time the JButton is clicked, hence parsing the text entered into the JTextField should be performed in the actionPerformed method.
JPanel panel = new JPanel();
panel.setLayout(null);
It is almost never needed to set the layout manager to null. You can almost always find an appropriate layout manager or you can place one JPanel within another and use different layout managers for each JPanel in order to get the desired placement of components within the Swing application window.
JButton doThing = new JButton("Do a Thing");
doThing.setActionCommand("Do a Thing");
By default, the text of a JButton is also its action command so no need to explicitly set it.
frame.setLocation(200, 200);
frame.setLocationRelativeTo(null);
These are two different ways to set the location of the JFrame and they do not complement each other. Use one or the other, but not both.
frame.setVisible(true);
Only after you have created all the [GUI] components and added them to the JFrame should you make the JFrame visible. So this should be the last line of the code that creates your GUI.
doThing.setBounds(250, 150, 100, 25);
If you use a layout manager, you never need to call method setBounds.
if(input != "0"){
This is not the way to compare strings. Use method equals as you have done here
if(check.equals("Do a Thing")){
Here is my rewrite of your application. Note that since I could not find the code for class MoneySorter, in your question, I just created my own version of that class. The point is to show how to change the text of the JLabel after clicking on the JButton and not how to create the actual text to display.
import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class MoneySorterRunner implements ActionListener {
private MoneySorter sorter = new MoneySorter();
private JTextField typeHere = new JTextField();
private JLabel num1;
private JLabel num2;
private JLabel num3;
private void createAndShowGui() {
JFrame frame = new JFrame("Money Calculator - v0.1a");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(false);
frame.add(createLabels(), BorderLayout.PAGE_START);
frame.add(createForm(), BorderLayout.CENTER);
frame.setSize(550, 250);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
private JPanel createForm() {
JPanel panel = new JPanel(new FlowLayout(FlowLayout.CENTER, 10, 0));
panel.setBorder(BorderFactory.createEmptyBorder(20, 0, 0, 0));
typeHere = new JTextField(10);
panel.add(typeHere);
JButton doThing = new JButton("Do a Thing");
doThing.addActionListener(this);
panel.add(doThing);
return panel;
}
private static JLabel createLabel(String text) {
JLabel label = new JLabel(text);
label.setFont(new Font("Arial", Font.PLAIN, 25));
return label;
}
private JPanel createLabels() {
JPanel panel = new JPanel(new GridLayout());
num1 = createLabel("num1");
panel.add(num1);
num2 = createLabel("num2");
panel.add(num2);
num3 = createLabel("num3");
panel.add(num3);
return panel;
}
public static void main(String args[]) {
new MoneySorterRunner().createAndShowGui();
}
public void actionPerformed(ActionEvent event){
String check = event.getActionCommand();
if(check.equals("Do a Thing")){
String text = typeHere.getText();
if (!text.isEmpty()) {
double money = Double.parseDouble(text);
num1.setText(sorter.divQuarter(money));
num2.setText(sorter.divQuarter(money));
num3.setText(sorter.divHalf(money));
}
}
}
}
class MoneySorter {
public String divQuarter(double money) {
return "divQuarter(" + money + ")";
}
public String divHalf(double money) {
return "divHalf(" + money + ")";
}
}
This is how your GUI looked when I ran your original code (as posted in your question).
This is how the GUI looks when running the code in this answer.
After launching
After entering a value and clicking the JButton

It looks like you forgot to set the ActionListener. You should also change your method to another name, because your method has the same name as the actionPerformed of the ActionListener.
doThing.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
new MoneySorterRunner().actionPerformedMethod(e);
}
});

You forgot to add the ActionListener.
In order to fix this, you need to do two things:
Add this statement to your code, preferably near where you create the button (so that it is easier to keep track). -
doThing.addActionListener(this);
When you write "public class", you also need this keyword: implements ActionListener - meaning your class (basically the first line) should look like:
public class MoneySorterRunner implements ActionListener
And that should make it work.

Java Swing: Components automatically change position when a certain component updates

I made a Java program and part of the program's function is to track the user's mouse X and Y coordinates.
The tracking works nicely but there's a small problem that bothers me.
When I move my mouse around the screen, the other components automatically change position.
Here's a MRE(Minimal Reproducible Example):
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.event.ActionListener;
public class Test {
static Timer t;
static JLabel label1;
static InnerTest inner;
static int mouseX;
static int mouseY;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
buildFrame();
runTimer();
}
});
}
public static void buildFrame() {
JFrame frame = new JFrame();
label1 = new JLabel("Test1");
JLabel label2 = new JLabel("Test Test");
JLabel label3 = new JLabel("Test Label Label");
JPanel panel = new JPanel();
panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
panel.add(label1);
panel.add(label2);
panel.add(label3);
label1.setAlignmentX(Component.CENTER_ALIGNMENT);
label2.setAlignmentX(Component.CENTER_ALIGNMENT);
label3.setAlignmentX(Component.CENTER_ALIGNMENT);
frame.getContentPane().add(panel);
frame.setSize(400, 200);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
public static void runTimer() {
inner = new InnerTest();
t = new Timer(20, inner);
t.start();
}
static class InnerTest implements ActionListener {
public void actionPerformed(ActionEvent e) {
mouseX = MouseInfo.getPointerInfo().getLocation().x * 100;
mouseY = MouseInfo.getPointerInfo().getLocation().y * 100;
label1.setText(" ( "+String.valueOf(mouseX)+" , "+String.valueOf(mouseY)+" )");
}
}
}
How do I keep the components still when another component is updating?

The components are added to the same panel so each is centered based on the maximum width of all three components. As the width of the top label changes the others are also adjusted.
The solution is to separate the top label from the other two labels.
One way would be:
//panel.add(label1);
panel.add(label2);
panel.add(label3);
//label1.setAlignmentX(Component.CENTER_ALIGNMENT);
label1.setHorizontalAlignment(JLabel.CENTER); // added
label2.setAlignmentX(Component.CENTER_ALIGNMENT);
label3.setAlignmentX(Component.CENTER_ALIGNMENT);
frame.add(label1, BorderLayout.PAGE_START); // added
frame.getContentPane().add(panel);

How to close JDialog and save the setting ?

Hi I'm working on a program and I faced a problem when I choose some settings from JDialog then click "ok", which is that the setting didn't save but come back to the original settings.
PS : I'm not English speaker so maybe you observe some mistakes in my text above.
picture
enter image description here
class DrawingSettingWindow extends JDialog {
public DrawingSettingWindow() {
this.setTitle("Drawing Setting Window");
this.setSize(550, 550);
this.setLocationRelativeTo(null);
this.setModal(true);
this.setLayout(new GridLayout(4, 1));
JLabel selectColorText = new JLabel("Select Drawing Color");
colorsList = new JComboBox(colors);
JPanel panel1 = new JPanel();
panel1.add(selectColorText);
panel1.add(colorsList);
add(panel1);
JLabel selectStyleText = new JLabel("Select Drawing Style");
JPanel panel2 = new JPanel();
normal = new JRadioButton("Normal");
normal.setSelected(true);
filled = new JRadioButton("Filled");
ButtonGroup bg = new ButtonGroup();
bg.add(normal);
bg.add(filled);
panel2.add(selectStyleText);
panel2.add(normal);
panel2.add(filled);
add(panel2);
JButton ok = new JButton("OK");
add(ok);
ok.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
setVisible(false);
}
});
this.pack();
this.setVisible(true);
}

The information is there, you just have to extract it from the dialog after the user is done using it. I would give the code above at least two new methods, one a public getColor() method that returns colorsList.getSelectedItem();, the color selection of the user (I'm not sure what type of object this is, so I can't show the method yet). Also another one that gets the user's filled setting, perhaps
public boolean getFilled() {
return filled.isSelected();
}
Since the dialog is modal, you'll know that the user has finished using it immediately after you set it visible in the calling code. And this is where you call the above methods to extract the data.
In the code below, I've shown this in this section: drawingSettings.setVisible(true);
// here you extract the data
Object color = drawingSettings.getColor();
boolean filled = drawingSettings.getFilled();
textArea.append("Color: " + color + "\n");
textArea.append("Filled: " + filled + "\n");
}
For example (see comments):
import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.Window;
import java.awt.Dialog.ModalityType;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
#SuppressWarnings("serial")
public class UseDrawingSettings extends JPanel {
private JTextArea textArea = new JTextArea(20, 40);
private DrawingSettingWindow drawingSettings;
public UseDrawingSettings() {
JPanel topPanel = new JPanel();
topPanel.add(new JButton(new ShowDrawSettings()));
setLayout(new BorderLayout());
add(new JScrollPane(textArea));
add(topPanel, BorderLayout.PAGE_START);
}
private class ShowDrawSettings extends AbstractAction {
public ShowDrawSettings() {
super("Get Drawing Settings");
}
#Override
public void actionPerformed(ActionEvent e) {
if (drawingSettings == null) {
Window win = SwingUtilities.getWindowAncestor(UseDrawingSettings.this);
drawingSettings = new DrawingSettingWindow(win);
}
drawingSettings.setVisible(true);
// here you extract the data
Object color = drawingSettings.getColor();
boolean filled = drawingSettings.getFilled();
textArea.append("Color: " + color + "\n");
textArea.append("Filled: " + filled + "\n");
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
private static void createAndShowGui() {
UseDrawingSettings mainPanel = new UseDrawingSettings();
JFrame frame = new JFrame("UseDrawingSettings");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
}
#SuppressWarnings("serial")
class DrawingSettingWindow extends JDialog {
private static final String TITLE = "Drawing Setting Window";
private JComboBox<String> colorsList;
private JRadioButton normal;
private JRadioButton filled;
// not sure what colors is, but I'll make it a String array for testing
private String[] colors = {"Red", "Orange", "Yellow", "Green", "Blue"};
public DrawingSettingWindow(Window win) {
super(win, TITLE, ModalityType.APPLICATION_MODAL);
// this.setTitle("Drawing Setting Window");
this.setSize(550, 550); // !! this is not recommended
this.setLocationRelativeTo(null);
this.setModal(true);
this.setLayout(new GridLayout(4, 1));
JLabel selectColorText = new JLabel("Select Drawing Color");
colorsList = new JComboBox(colors);
JPanel panel1 = new JPanel();
panel1.add(selectColorText);
panel1.add(colorsList);
add(panel1);
JLabel selectStyleText = new JLabel("Select Drawing Style");
JPanel panel2 = new JPanel();
normal = new JRadioButton("Normal");
normal.setSelected(true);
filled = new JRadioButton("Filled");
ButtonGroup bg = new ButtonGroup();
bg.add(normal);
bg.add(filled);
panel2.add(selectStyleText);
panel2.add(normal);
panel2.add(filled);
add(panel2);
JButton ok = new JButton("OK");
add(ok);
ok.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
setVisible(false);
}
});
this.pack();
// this.setVisible(true); // this should be the calling code's responsibility
}
public Object getColor() {
return colorsList.getSelectedItem();
}
public boolean getFilled() {
return filled.isSelected();
}
public static void main(String[] args) {
JFrame frame = new JFrame("Foo");
}
}
Side notes:
I've changed your class's constructor to accept a Window parameter, the base class for JFrame, JDialog, and such, and have added a call to the super's constructor. This way, the dialog is a true child window of the calling code (or you can pass in null if you want it not to be).
I recommend not making the dialog visible within its constructor. It is the calling code's responsibility for doing this, and there are instances where the calling code will wish to not make the dialog visible after creating it, for example if it wanted to attach a PropertyChangeListener to it before making it visible. This is most important for modal dialogs, but is just good programming practice.
I didn't know the type of objects held by your combo box, and so made an array of String for demonstration purposes.

Alignment of RadioButtons in Java GUI

Here is what my program is suppose to look like:
but I can't seem to get my radio buttons and my JLabel to be aligned properly. How do I align my radio buttons on the right and stacked? Also, how do I get my JLabel and JTextField to show stacked?
Here is my code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SeriesCalc extends JFrame {
private final int WIDTH = 300;
private final int HEIGHT = 300;
private JFrame frame = new JFrame("Recursion");
private JPanel panel = new JPanel();
private JPanel labels = new JPanel();
private JPanel buttons = new JPanel();
private JPanel radioButtonsPanel = new JPanel();
private JLabel inputLabel = new JLabel("Enter i:");
private JLabel resultLabel = new JLabel("Result:");
private JTextField inputField = new JTextField(15);
private JTextField resultField = new JTextField(15);
private JButton compute = new JButton("Compute");
private JRadioButton iterative, recursive;
public SeriesCalc() {
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
radioButtonsPanel.add(iterative = new JRadioButton("Iterative"));
radioButtonsPanel.add(recursive = new JRadioButton("Recursive"));
add(radioButtonsPanel);
ButtonGroup radioButtons = new ButtonGroup();
radioButtons.add(iterative);
radioButtons.add(recursive);
iterative.addActionListener(new Calculations());
recursive.addActionListener(new Calculations());
compute.addActionListener(new Calculations());
resultField.setEditable(false);
panel.setLayout(new GridLayout(4, 1));
labels.add(inputLabel);
labels.add(inputField);
labels.add(resultLabel);
labels.add(resultField);
buttons.add(compute);
panel.add(radioButtonsPanel);
panel.add(labels);
panel.add(buttons);
frame.getContentPane().add(panel);
}
public void display() {
frame.setSize(WIDTH, HEIGHT);
frame.setVisible(true);
}
public class Calculations implements ActionListener {
public void actionPerformed(ActionEvent e) {
Object calc = e.getSource();
try {
if (calc == compute) {
if (iterative.isSelected()) {
double n = Double.parseDouble(inputField.getText());
double product = 1;
for (int i = 3; i < n; i++) {
product *= i;
}
resultField.setText(Double.toString(product));
} else if (recursive.isSelected()) {
double i = Double.parseDouble(inputField.getText());
double y = 0;
if (i == 1) {
resultField.setText(Double.toString(i / (2. * i + 1)));
} else {
resultField.setText(Double.toString(i / (2. * i + 1)+ (i -1)));
}
}
}
} catch (NumberFormatException nfe) {
System.err.println(nfe.getMessage());
}
}
}
public static void main(String[] args) {
SeriesCalc calculator = new SeriesCalc();
calculator.display();
}
}

I see some errors in your program:
You're extending JFrame and creating an instance of it in the same program. Use one or the other (I recommend the latter), See Using extends vs calling it inside of class.
You're setting frame.setSize() while this isn't an error it's always better to call frame.pack() in your program. It will respect the minimum size where all the components are shown in their preferredSizes. If you need an exact size for your window override getPreferredSize() method instead.
You're not placing your program on the Event Dispatch Thread (EDT), this could cause threading issues in the future as Swing is not thread safe, this can be solved with:
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
//Call your constructor here
}
});
}
but I can't seem to get my radio buttons and my JLabel to be aligned properly
This is because a JPanel's default layout manager is FlowLayout and thus it will place your components in a single row.
My idea to get to your desired GUI was to use a single GridLayout with 0 rows (it will add as many as needed) and 2 columns, and where you need a "blank" space you can add empty JLabels.
I didn't placed an ActionListener on my code as this question is about the GUI design not the logic inside it.
I think I'm not missing anything, this is the output that the below code creates:
import java.awt.GridLayout;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class SeriesCalc {
private JFrame frame;
private JRadioButton iterative;
private JRadioButton recursive;
private ButtonGroup group;
private JLabel label;
private JLabel resultLabel;
private JTextField field;
private JTextField resultField;
private JButton computeButton;
private JPanel pane;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new SeriesCalc().createAndShowGui();
}
});
}
public void createAndShowGui() {
frame = new JFrame(getClass().getSimpleName());
pane = new JPanel();
pane.setLayout(new GridLayout(0, 2, 2, 5));
iterative = new JRadioButton("Iterative");
recursive = new JRadioButton("Recursive");
group = new ButtonGroup();
group.add(iterative);
group.add(recursive);
computeButton = new JButton("Compute");
label = new JLabel("Enter \"i\": ");
resultLabel = new JLabel("Result: ");
field = new JTextField(5);
resultField = new JTextField(5);
resultField.setEnabled(false);
pane.add(new JLabel(""));
pane.add(iterative);
pane.add(new JLabel(""));
pane.add(recursive);
pane.add(label);
pane.add(field);
pane.add(new JLabel(""));
pane.add(computeButton);
pane.add(resultLabel);
pane.add(resultField);
frame.add(pane);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}

I don´t know if you are using an IDE like Eclipse or NetBeans. In Eclipse for example, you can open this class with windowbuilder and you could visualize how your Frame will appear. Obviously you can move element in this view (window builder) and put all objects where you want and the size you want. In the next image you could see the view of an edit of a Frame if you open it with window builder in mode design in Eclipse. In this mode (design) you can put absolute layout to these objects and they can be put where you want with that layout. I recommend you to use an IDE like eclipse for Java Developing, it is very useful and it has a lot of facilities. I hope I could help you:
enter image description here

Display a window to obtain user input

I'm new to programming with Java.
I have these two small projects.
import javax.swing.*;
public class tutorial {
public static void main(String[] args){
JFrame frame = new JFrame("Test");
frame.setVisible(true);
frame.setSize(300,300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel label = new JLabel("hello");
JPanel panel = new JPanel();
frame.add(panel);
panel.add(label);
JButton button = new JButton("Hello again");
panel.add(button);
}
}
and this one:
import java.util.*;
public class Test {
public static void main(String[] args){
int age;
Scanner keyboard = new Scanner(System.in);
System.out.println("How old are you?");
age = keyboard.nextInt();
if (age<18)
{
System.out.println("Hi youngster!");
}
else
{
System.out.println("Hello mature!");
}
}
}
How can I add the second code to the first one, so that the user will see a window that says 'How old are you' and they can type their age.
Thanks in advance!

I'm not sure of all the things you wanted because it was undefined, but as I far as I understand, you wanted a JFrame containing an input field, in which you will be able to input values and display the appropriate answer.
I also suggest you read tutorial , but don't hesitate if you have question.
I hope it's a bit close to what you wanted.
package example.tutorial;
import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class Tutorial extends JPanel {
private static final String YOUNG_RESPONSE = "Hi youngster!";
private static final String ADULT_RESPONSE = "Hello mature!";
private static final String INVALID_AGE = "Invalid age!";
private static final int MIN_AGE = 0;
private static final int MAX_AGE = 100;
private static JTextField ageField;
private static JLabel res;
private Tutorial() {
setLayout(new BorderLayout());
JPanel northPanel = new JPanel();
northPanel.setLayout(new FlowLayout());
JLabel label = new JLabel("How old are you ? ");
northPanel.add(label);
ageField = new JTextField(15);
northPanel.add(ageField);
add(northPanel, BorderLayout.NORTH);
JPanel centerPanel = new JPanel();
JButton btn = new JButton("Hello again");
btn.addActionListener(new BtnListener());
centerPanel.add(btn);
res = new JLabel();
res.setVisible(false);
centerPanel.add(res);
add(centerPanel, BorderLayout.CENTER);
}
public static void main(String[] args) {
JFrame frame = new JFrame("Test");
frame.add(new Tutorial());
frame.setVisible(true);
frame.setSize(300, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
private static class BtnListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
String content = ageField.getText();
int age = -1;
try{
age = Integer.parseInt(content);
if(isValid(age)) {
res.setText(age < 18 ? YOUNG_RESPONSE : ADULT_RESPONSE);
} else {
res.setText(INVALID_AGE);
}
if(!res.isVisible())
res.setVisible(true);
} catch(NumberFormatException ex) {
res.setText("Wrong input");
}
}
private boolean isValid(int age) {
return age > MIN_AGE && age < MAX_AGE;
}
}
}

so that the user will see a window that says 'How old are you' and they can type their age.
The easiest way to start would be to use a JOptionPane. Check out the section from the Swing tutorial on How to Use Dialogs for examples and explanation.
Don't forget to look at the table of contents for other Swing related topics for basic information about Swing.

You will need an input field to get the text and then add an ActionListener to the button which contains the logic that is performed when the button is pressed.
I modified your code to implement what you described:
import javax.swing.*;
import java.awt.event.*;
public class tutorial {
public static void main(String[] args) {
JFrame frame = new JFrame("Test");
frame.setVisible(true);
frame.setSize(300, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel label = new JLabel("hello");
JPanel panel = new JPanel();
frame.add(panel);
panel.add(label);
final JTextField input = new JTextField(5); // The input field with a width of 5 columns
panel.add(input);
JButton button = new JButton("Hello again");
panel.add(button);
final JLabel output = new JLabel(); // A label for your output
panel.add(output);
button.addActionListener(new ActionListener() { // The action listener which notices when the button is pressed
public void actionPerformed(ActionEvent e) {
String inputText = input.getText();
int age = Integer.parseInt(inputText);
if (age < 18) {
output.setText("Hi youngster!");
} else {
output.setText("Hello mature!");
}
}
});
}
}
In that example we don't validate the input. So if the input is not an Integer Integer.parseInt will throw an exception. Also the components are not arranged nicely. But to keep it simple for the start that should do it. :)

it's not an easy question since you are working on command line in one example, and in a Swing GUI in the other.
Here's a working example, i've commented here and there.
This is no where near java best practises and it misses a lot of validation (just see what happens when you enter a few letters or nothing in the textfield.
Also please ignore the setLayout(null) and setBounds() statements, it's just a simple example not using any layout managers.
I hope my comments will help you discovering java!
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
//You'll need to implement the ActionListener to listen to buttonclicks
public class Age implements ActionListener{
//Declare class variables so you can use them in different functions
JLabel label;
JTextField textfield;
//Don't do al your code in the static main function, instead create an instance
public static void main(String[] args){
new Age();
}
// this constructor is called when you create a new Age(); like in the main function above.
public Age()
{
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(300,300);
frame.setLayout(null);
JPanel panel = new JPanel();
panel.setBounds(0,0,300,300);
panel.setLayout(null);
label = new JLabel("hello");
label.setBounds(5,5,100,20);
// a JTextfield allows the user to edit the text in the field.
textfield = new JTextField();
textfield.setBounds(5,30,100,20);
JButton button = new JButton("Hello again");
button.setBounds(130,30,100,20);
// Add this instance as the actionlistener, when the button is clicked, function actionPerformed will be called.
button.addActionListener(this);
panel.add(label);
panel.add(textfield);
panel.add(button);
frame.add(panel);
frame.setVisible(true);
}
//Required function actionPerformed for ActionListener. When the button is clicked, this function is called.
#Override
public void actionPerformed(ActionEvent e)
{
// get the text from the input.
String text = textfield.getText();
// parse the integer value from the string (! needs validation for wrong inputs !)
int age = Integer.parseInt(text);
if (age<18)
{
//instead of writing out, update the text of the label.
label.setText("Hi youngster!");
}
else
{
label.setText("Hello mature!");
}
}
}