Learn CODENAME-ONE with Real Code Examples

import com.codename1.ui.*;
import com.codename1.ui.layouts.BoxLayout;

public class TodoApp extends Form {
    private DefaultListModel<String> todos = new DefaultListModel<>();
    private List todoList;
    private TextField newTodo;

    public TodoApp() {
        setTitle("Todo App");
        setLayout(new BoxLayout(BoxLayout.Y_AXIS));

        newTodo = new TextField("", "New Todo");
        Button addButton = new Button("Add");
        todoList = new List(todos);

        addButton.addActionListener(e -> {
        if(!newTodo.getText().trim().isEmpty()){
        todos.addItem(newTodo.getText().trim());
        newTodo.clear();
        }
        });

        addAll(newTodo, addButton, todoList);
    }

    public void start() {
        show();
    }
}

Demonstrates a simple Codename One app with a Todo list, adding tasks, and displaying them using native UI components.

import com.codename1.ui.*;
import com.codename1.ui.layouts.FlowLayout;

public class CounterApp extends Form {
    private int count = 0;
    private Label counterLabel;

    public CounterApp() {
        setTitle("Counter App");
        setLayout(new FlowLayout(Component.CENTER));

        counterLabel = new Label("0");
        Button inc = new Button("+");
        Button dec = new Button("-");

        inc.addActionListener(e -> update(++count));
        dec.addActionListener(e -> update(--count));

        addAll(dec, counterLabel, inc);
    }

    private void update(int value) {
        counterLabel.setText(String.valueOf(value));
        revalidate();
    }
}

Demonstrates a simple counter app with increment and decrement buttons in Codename One.

import com.codename1.ui.*;
import com.codename1.ui.layouts.BoxLayout;

public class LoginApp extends Form {
    public LoginApp() {
        setTitle("Login");
        setLayout(new BoxLayout(BoxLayout.Y_AXIS));

        TextField username = new TextField("", "Username");
        TextField password = new TextField("", "Password", 20, TextField.PASSWORD);
        Button loginBtn = new Button("Login");

        loginBtn.addActionListener(e -> Dialog.show("Info", "Welcome, " + username.getText(), "OK", null));

        addAll(username, password, loginBtn);
    }
}

Shows a simple login form with username and password fields using Codename One UI components.

import com.codename1.ui.*;
import com.codename1.ui.layouts.BoxLayout;
import com.codename1.io.Preferences;

public class NotesApp extends Form {
    private TextArea noteArea;

    public NotesApp() {
        setTitle("Notes");
        setLayout(new BoxLayout(BoxLayout.Y_AXIS));

        noteArea = new TextArea(Preferences.get("note", ""));
        Button save = new Button("Save");

        save.addActionListener(e -> {
        Preferences.set("note", noteArea.getText());
        Dialog.show("Saved", "Note saved successfully!", "OK", null);
        });

        addAll(noteArea, save);
    }
}

Demonstrates a basic notes app that saves and loads notes using Preferences API.

import com.codename1.ui.*;
import com.codename1.ui.layouts.FlowLayout;

public class StopwatchApp extends Form {
    private int seconds = 0;
    private Label timeLabel;
    private com.codename1.ui.util.UITimer timer;

    public StopwatchApp() {
        setTitle("Stopwatch");
        setLayout(new FlowLayout(Component.CENTER));

        timeLabel = new Label("00:00");
        Button start = new Button("Start");
        Button stop = new Button("Stop");
        Button reset = new Button("Reset");

        timer = new com.codename1.ui.util.UITimer(() -> {
        seconds++;
        timeLabel.setText(String.format("%02d:%02d", seconds / 60, seconds % 60));
        revalidate();
        });

        start.addActionListener(e -> timer.schedule(1000, true, this));
        stop.addActionListener(e -> timer.cancel());
        reset.addActionListener(e -> { seconds = 0; timeLabel.setText("00:00"); });

        addAll(timeLabel, start, stop, reset);
    }
}

Implements a simple stopwatch with start, stop, and reset using Codename One Timer.

import com.codename1.ui.*;
import com.codename1.ui.layouts.BorderLayout;
import com.codename1.ui.URLImage;

public class ImageViewerApp extends Form {
    public ImageViewerApp() {
        setTitle("Image Viewer");
        setLayout(new BorderLayout());

        Image placeholder = Image.createImage(100, 100);
        URLImage img = URLImage.createToStorage(placeholder, "sample", "https://picsum.photos/200");
        Label imageLabel = new Label(img);

        add(BorderLayout.CENTER, imageLabel);
    }
}

Loads and displays an image from URL using Codename One's URLImage.

import com.codename1.ui.*;
import com.codename1.ui.layouts.BoxLayout;

public class ThemeApp extends Form {
    private boolean darkMode = false;

    public ThemeApp() {
        setTitle("Theme Switcher");
        setLayout(new BoxLayout(BoxLayout.Y_AXIS));

        Button toggle = new Button("Toggle Theme");
        Label label = new Label("Light Mode Active");

        toggle.addActionListener(e -> {
        darkMode = !darkMode;
        UIManager.getInstance().setThemeProps(UIManager.getInstance().getTheme(darkMode ? "dark" : "light"));
        label.setText(darkMode ? "Dark Mode Active" : "Light Mode Active");
        revalidate();
        });

        addAll(label, toggle);
    }
}

Demonstrates theme switching (light/dark mode) in Codename One.

import com.codename1.ui.*;
import com.codename1.ui.layouts.GridLayout;

public class CalculatorApp extends Form {
    private TextField input;
    private double current = 0;
    private String op = "";

    public CalculatorApp() {
        setTitle("Calculator");
        setLayout(new BoxLayout(BoxLayout.Y_AXIS));

        input = new TextField();
        Container grid = new Container(new GridLayout(4, 4));
        String[] buttons = {"7", "8", "9", "/", "4", "5", "6", "*", "1", "2", "3", "-", "0", ".", "=", "+"};

        for(String b : buttons) {
        Button btn = new Button(b);
        btn.addActionListener(e -> handleInput(b));
        grid.add(btn);
        }

        addAll(input, grid);
    }

    private void handleInput(String val) {
        if("0123456789.".contains(val)) input.setText(input.getText() + val);
        else if("+-*/".contains(val)) { current = Double.parseDouble(input.getText()); op = val; input.clear(); }
        else if(val.equals("=")) {
        double second = Double.parseDouble(input.getText());
        switch(op) {
        case "+": current += second; break;
        case "-": current -= second; break;
        case "*": current *= second; break;
        case "/": current /= second; break;
        }
        input.setText(String.valueOf(current));
        }
    }
}

Implements a minimal calculator performing basic arithmetic in Codename One.

import com.codename1.ui.*;
import com.codename1.ui.layouts.BoxLayout;
import com.codename1.io.*;

public class WeatherApp extends Form {
    public WeatherApp() {
        setTitle("Weather App");
        setLayout(new BoxLayout(BoxLayout.Y_AXIS));

        TextField city = new TextField("", "Enter City");
        Button fetch = new Button("Fetch");
        Label result = new Label();

        fetch.addActionListener(e -> {
        ConnectionRequest req = new ConnectionRequest();
        req.setUrl("https://api.weatherapi.com/v1/current.json?key=demo&q=" + city.getText());
        req.addResponseListener(res -> {
        String data = new String(req.getResponseData());
        result.setText(data.substring(0, Math.min(100, data.length())) + "...");
        revalidate();
        });
        NetworkManager.getInstance().addToQueue(req);
        });

        addAll(city, fetch, result);
    }
}

Fetches weather data using a REST API and displays results in Codename One.

import com.codename1.ui.*;
import com.codename1.media.*;
import java.io.IOException;

public class QRScannerApp extends Form {
    public QRScannerApp() {
        setTitle("QR Scanner");
        setLayout(new BorderLayout());

        Button scan = new Button("Scan QR");
        Label result = new Label();

        scan.addActionListener(e -> {
        try {
        Capture.capturePhoto((path) -> result.setText("Scanned file: " + path));
        } catch (Exception ex) {
        Dialog.show("Error", ex.getMessage(), "OK", null);
        }
        });

        add(BorderLayout.CENTER, scan);
        add(BorderLayout.SOUTH, result);
    }
}

Demonstrates scanning a QR code using Codename One's built-in CameraKit.