piecetable

Piece table data structure in Java.

Piece table is a data structure typically used to represent a text document editing.

Operations of piece table

Initial state

A piece table consists of three columns:

• Which buffer
• Start index in the buffer
• Length in the buffer

In addition to the table, two buffers are used to handle edits:

• read-only : A reference to the original text document
• append-only : A buffer to a temporary file

Insert

Inserting characters to the text consists of:

• Appending characters to the read-only buffer, and
• Updating the entry in piece table (breaking an entry into two or three)

Delete

Single character deletion can be one of two possible conditions:

• The deletion is at the start or end of a piece entry, in which case the appropriate entry in piece table is modified.
• The deletion is in the middle of a piece entry, in which case the entry is split then one of the successor entries is modified as above.

Usage

Add dependencies.

dependencies {
    implementation("com.mammb:piecetable:0.6.3")
}

There are three classes.

• PieceTable - Primitive piece table implantation by bytes
• Document - Text manipulation with row-column number and charset infer
• TextEdit - Advanced text editing abstraction, with undo/redo, and more

Use TextEdit in most cases.

PieceTable

var pt = PieceTable.of();

pt.insert(0, "a large text".getBytes());
pt.insert(8, "span of ".getBytes());
pt.delete(1, 6);

var bytes = pt.get(0, (int) pt.length());
assertEquals("a span of text", new String(bytes));

Document

var doc = Document.of();

doc.insert(0, 0, "a large text"); // row:0 col:0
doc.insert(0, 8, "span of ");     // row:0 col:8
doc.delete(0, 1, 6);              // row:0 col:1

var text = doc.getText(0);        // get the text of row:0
assertEquals("a span of text", text);

To load an existing file, use the following

var path = Path.of("sample.txt");
var doc = Document.of(path);

The charset is inferred from the loaded file, but can also be specified explicitly.

var doc = Document.of(path, Charset.forName("xxx"));

CharsetMatch can also be used to customize charset infer.

CharsetMatch customCharsetMatch = // ...
var doc = Document.of(path, customCharsetMatch);

TextEdit

var edit = TextEdit.of();

edit.insert(0, 0, "a large text");
edit.insert(0, 8, "span of ");
edit.delete(0, 1, 6);
assertEquals("a span of text", edit.getText(0));

edit.undo();
assertEquals("a large span of text", edit.getText(0));

edit.redo();
assertEquals("a span of text", edit.getText(0));

How to run the example application

./gradlew build
cd examples/fx-editor
./gradlew run

This example is merely a simple demonstration. For more practical applications, please refer to the following.

Sample applications using this library

• min-editor