JEditor — Terminal-Based Text Editor

JEditor is a terminal-based text editor inspired by the classic edit-style workflow. A terminal editor must do more than read a line from standard input: it needs to interpret keyboard input, maintain document state, position the cursor, render only the visible viewport, and coordinate commands such as open, save, search and navigation. The project is useful for studying how a user-facing terminal application can be decomposed into focused subsystems.

The Maven project targets Java 22 and uses JLine for terminal interaction. The POM configures compiler, test and executable-jar/shaded-jar packaging. JUnit 5 dependencies support automated tests. JLine provides lower-level terminal capabilities so the application can manage terminal input and output without treating the editor as a simple line-oriented console program.

The repository separates App, EditorLauncher, HelpPrinter, Version and ExitCode from the editor's core behaviour. CommandLineParser turns command-line arguments into EditorOptions, keeping CLI parsing out of the editing engine. This makes the application entry point responsible for launching the editor with a configuration rather than mixing command syntax with document manipulation.

The Document class represents the content being edited and the state associated with file operations. The Editor and EditorApplication coordinate editing behaviour, while Cursor represents the current logical location. Keeping document content separate from terminal coordinates matters because a character's position in the file is not always the same as its position on the visible screen. A long line can extend beyond the terminal width, and a document can contain more lines than fit on the screen.

The repository contains EditorLayout, EditorLayoutCalculator, DocumentPosition, ScreenPosition, ViewPort and ViewportController. This separation is important in terminal software. DocumentPosition describes where the cursor or content belongs in the document, while ScreenPosition describes where it appears in the terminal. The viewport maps a window of the larger document onto the available terminal area. Horizontal and vertical scrolling update that mapping without changing the underlying document content.

The search package contains SearchEngine, SearchController, SearchState, SearchOptions, SearchResult, SearchBounds, SearchFocus and layout/mouse controller classes. The changelog records incremental search, exact matching, case-sensitive search, navigation between matches and a result counter. Separating the search engine from its state and UI controller keeps matching logic distinct from how the editor displays and navigates results. Boundary handling is particularly important when the document changes while a search is active.

The changelog records open, save and Save As support, a dialog framework, an About dialog, confirmation dialogs and unsaved-change protection. It also records file information in the status bar and a message-bar timeout. These features introduce important state transitions: a document can be modified, saved, redirected to another path or closed only after a confirmation decision. Keeping these transitions explicit prevents accidental data loss and makes the editor easier to reason about.

The changelog records tests for search, search navigation, viewport scrolling, Go To Line and line merging, along with an expanded editor test suite. This is a useful example of testing behaviour at subsystem boundaries. Search tests should verify match ranges and boundary handling; viewport tests should verify how cursor movement changes the visible region; file tests should cover missing paths and save behaviour. Small tests make terminal interaction code safer to evolve.

JEditor demonstrates why even a relatively small terminal tool benefits from boundaries between CLI parsing, document state, editing commands, layout, viewport navigation, search and terminal I/O. This is not a claim that the project is an operating-system editor or a complete replacement for a graphical IDE. It is a focused terminal application whose internal responsibilities can be studied and extended independently.