Design Philosophy of Jexer

  

Building applications for the terminal traditionally required developers to manage many low-level details such as cursor positioning, screen refresh logic, keyboard input handling, and manual drawing of text elements. This often made terminal application development complex and error-prone. Libraries like Jexer were created to simplify this process by providing a structured framework for building rich terminal applications.

 

The design philosophy of Jexer focuses on bringing modern application design principles to terminal environments. Instead of treating the terminal as a simple output stream, Jexer treats it as a full application environment capable of hosting windows, widgets, dialogs, and interactive components.

 

The core idea behind Jexer is to allow developers to build desktop-style applications that run inside a terminal while hiding the complexity of terminal rendering and input management.

 

1. Goals of Jexer

The primary goal of Jexer is to make it easier for Java developers to build powerful and structured terminal applications.

 

Some of the key goals include:

 

·      Simplifying terminal UI development

·      Providing reusable UI components

·      Supporting complex application layouts

·      Handling keyboard and mouse events automatically

 

Allowing developers to focus on application logic rather than terminal internals

 

Instead of manually writing ANSI escape sequences and managing terminal buffers, developers can use high-level components such as windows, menus, text fields, and dialogs.

 

This approach significantly reduces development complexity and improves maintainability.

 

2. Window-Based Terminal Applications

One of the most distinctive aspects of Jexer is its window-based interface model.

 

Traditional terminal applications usually display information in a single screen layout. In contrast, Jexer allows developers to create multiple windows that behave similarly to windows in a graphical desktop environment.

 

These windows can:

 

·      be opened and closed dynamically

·      contain different UI components

·      overlap with other windows

·      be moved or resized by the user

 

This design enables developers to build applications that feel very similar to desktop software, even though they run entirely inside a terminal.

 

For example, a Jexer application could include:

 

·      a dashboard window showing system metrics

·      a log viewer window displaying real-time logs

·      a configuration dialog for modifying settings

 

Each of these elements can operate independently within the terminal environment.

 

3. Event-Driven Architecture

Another important design principle used by Jexer is event-driven architecture.

 

Instead of continuously polling for input or manually handling keyboard events, Jexer processes user interactions through events.

 

Common events include:

 

·      key presses

·      mouse clicks

·      window focus changes

·      menu selections

·      dialog interactions

 

When an event occurs, Jexer automatically dispatches it to the appropriate component. Developers simply implement event handlers to respond to user actions.

 

This model is very similar to how graphical frameworks handle user interactions, making it easier for developers who are familiar with GUI development.

 

4. Separation of UI and Logic

A key principle in modern software design is the separation of user interface and application logic. Jexer encourages this approach by providing structured components that manage UI rendering and interaction.

 

With this design, developers can:

 

·      define UI components such as windows and dialogs

·      attach event handlers to respond to user actions

·      implement application logic separately from UI code

 

This separation improves code organization and makes applications easier to maintain and extend.

 

For example, a monitoring application might display system metrics in a window, while the logic responsible for retrieving those metrics runs independently in the background.

 

5. Terminal and Swing Support

An interesting feature of Jexer is its ability to run applications in both terminal environments and Java Swing windows.

 

This means the same application can operate in two different modes:

 

·      Inside a terminal window

·      Inside a graphical window using Swing

 

This dual capability allows developers to test and run their applications even in environments where a terminal interface may not be ideal.

 

It also demonstrates how Jexer bridges the gap between terminal based applications and graphical interfaces.

 

6. Bringing Desktop UI Concepts to the Terminal

Perhaps the most interesting aspect of Jexer’s design philosophy is its attempt to bring desktop style user interface concepts into the terminal.

 

Traditional terminal applications are often limited to simple menus or command-driven interfaces. Jexer expands this concept by introducing familiar UI patterns such as:

 

·      window managers

·      dialog boxes

·      menu bars

·      status bars

·      interactive widgets

 

These components allow developers to create terminal applications that behave very similarly to graphical desktop software.

 

The result is a powerful hybrid environment where applications retain the efficiency and portability of terminal programs while offering the usability and structure of graphical interfaces.

 

Find the below working Application.

 

JexerConceptDemo.java

package com.sample.app.chapter3;

import jexer.TAction;
import jexer.TApplication;
import jexer.TMessageBox;
import jexer.TStatusBar;
import jexer.TWindow;
import jexer.event.TMenuEvent;
import jexer.menu.TMenu;

public class JexerConceptDemo extends TApplication {

    private static final int MENU_EXIT = 100;
    private static final int MENU_ABOUT = 200;
    private static final int MENU_OPEN_LOG = 300;
    private static final int MENU_CLOSE_LOG = 400;

    // Keep reference to log window
    private TWindow logWindow = null;

    public JexerConceptDemo() throws Exception {

        super(TApplication.BackendType.SWING);

        createMenuBar();
        createDashboardWindow();
        createStatusBar();
    }

    private void createMenuBar() {

        TMenu fileMenu = addMenu("&File");
        fileMenu.addItem(MENU_OPEN_LOG, "&Open Log Viewer");
        fileMenu.addItem(MENU_CLOSE_LOG, "&Close Log Viewer");
        fileMenu.addItem(MENU_EXIT, "E&xit");

        addMenu("&Help")
            .addItem(MENU_ABOUT, "&About");
    }

    private void createDashboardWindow() {

        TWindow dashboard = addWindow("System Dashboard", 2, 2, 60, 15);

        dashboard.addLabel("CPU Usage: 32%", 2, 2);
        dashboard.addLabel("Memory: 4.1 GB / 16 GB", 2, 4);
        dashboard.addLabel("Active Connections: 12", 2, 6);

        dashboard.addLabel("Use File menu to open/close Log Viewer", 2, 9);
        dashboard.addLabel("Windows can overlap and move", 2, 10);
    }

    private void createStatusBar() {

        TWindow mainWindow = getActiveWindow();

        TStatusBar statusBar = mainWindow.newStatusBar(
            "Demo: Window UI | File → Open Log Viewer"
        );
    }

    private void openLogWindow() {

        // Prevent multiple log windows
        if (logWindow != null) {
            activateWindow(logWindow);
            return;
        }

        logWindow = addWindow("Application Logs", 10, 5, 50, 12);

        logWindow.addLabel("[INFO] Application started", 2, 2);
        logWindow.addLabel("[INFO] Connected to server", 2, 3);
        logWindow.addLabel("[WARN] CPU usage slightly high", 2, 4);
        logWindow.addLabel("[INFO] Monitoring active", 2, 5);

        // Close button
        logWindow.addButton("Close", 2, 8, new TAction() {
            public void DO() {
                closeLogWindow();
            }
        });
    }

    private void closeLogWindow() {

        if (logWindow != null) {
            closeWindow(logWindow);
            logWindow = null;
        }
    }

    @Override
    protected boolean onMenu(TMenuEvent event) {

        if (event.getId() == MENU_EXIT) {

            TMessageBox confirm = messageBox(
                "Exit",
                "Do you really want to exit?",
                TMessageBox.Type.YESNO
            );

            if (confirm.isYes()) {
                exit();
            }

            return true;
        }

        if (event.getId() == MENU_ABOUT) {

            messageBox(
                "About",
                "Jexer Demo Application\n" +
                "Shows window UI, menus and events\n" +
                "Running inside a terminal",
                TMessageBox.Type.OK
            );

            return true;
        }

        if (event.getId() == MENU_OPEN_LOG) {

            openLogWindow();
            return true;
        }

        if (event.getId() == MENU_CLOSE_LOG) {

            closeLogWindow();
            return true;
        }

        return super.onMenu(event);
    }

    public static void main(String[] args) throws Exception {

        JexerConceptDemo app = new JexerConceptDemo();
        app.run();
    }
}

Output

Previous                                                    Next                                                    Home