Question

JAVA DATA STRUCTURES

Write a line-based text editor. The command syntax is similar to the Unix line editor ed. The internal copy of the file is maintained as a linked list of lines. To be able to go up and down in the file, you have to maintain a doubly linked list. Most commands are represented by a one-character string. Some are two characters and require an argument (or two). Support the commands shown below:

Command Function Go to the top. Add text after current line until on its own line Delete current line Delete several lines. Change name of the current file (for next write) Go to a numbered line. Get help Like append, but add lines before current line. Move current line after some other line. dr num num f name gnum m num mr num num num Move several lines as a unit after some other line Toggle whether line numbers are displayed. Print current line Print several lines. Abort without write. Read and paste another file into the current file. Substitute text with other text. Copy current line to after some other line. Copy several lines to after some other line. Write file to disk. Exit with write Go to the last line Go up one line. Go down one line Print current line number. Search forward for a pattern. Search backward for a pattern. Print number of lines and characters in file pr num num q! r name s text text t num tr num num num x! / text ? text

Answer 1

TextEditor.java
import java.util.Iterator;
import java.io.*;

import WattBrown.LinkedList;

public class TextEditor {

// Each TextEditor object represents a text subject to editing. The text
// consists of lines numbered 0, 1, �. If the text is nonempty, at any time
// one line is selected, initially line 0.

// This text is represented as a list of lines, text. The number of the
// currently-selected line (or -1 if the text is empty) is held in selection.
private LinkedList text;
private int selection;

public TextEditor () {
// Construct a text, initially empty.
text = new LinkedList();
selection = -1;
}

public void insertBefore (String line) {
// Insert line immediately before the selected line in this text.
if (selection < 0) {
warn("There is no line to insert before."); return;
}
text.add(selection++, line);
}

public void insertAfter (String line) {
// Insert line immediately after the selected line in this text, and select the
// inserted line.
text.add(++selection, line);
}

public void delete () {
// Delete the selected line in this text, and select the following line (or the
// previous line, if the last line was deleted).
if (selection < 0) {
warn("There is no line to delete."); return;
}
text.remove(selection);
if (selection == text.size())
selection--;
}

public void replace (String line) {
// Replace the selected line in this text by line, and select the replacement
// line.
if (selection < 0) {
warn("There is no line to replace."); return;
}
text.set(selection, line);
}

public void select (int ln) {
// Select the line numbered ln in this text.
if (ln < 0 || ln >=text.size())
warn("There is no such line to select.");
selection = ln;
}

public void find (String s) {
// Find the first line, between the selected line and the end of this text, that
// contains s as a substring, and select that line.
if (selection < 0) {
warn("There are no lines to search."); return;
}
int length = text.size();
for (int ln = selection; ln < length; ln++) {
String line = (String) text.get(ln);
if (line.indexOf(s) >= 0) {
selection = ln;
return;
}
}
warn("There is no line containing '" + s + "'.");
}

public void load (BufferedReader input)
throws IOException {
// Insert the text contained in input after the last line of this text, and
// select the last line inserted.
for (;;) {
String line = input.readLine();
if (line == null) break;
text.add(line);
}
selection = text.size()-1;
}

public void save (BufferedWriter output)
throws IOException {
// Write this text to output.
Iterator lines = text.iterator();
while (lines.hasNext()) {
String line = (String) lines.next();
output.write(line + '\n');
}
}

public void display () {
// Display this text, highlighting the selected line.
int ln = 0; // � line number
Iterator lines = text.iterator();
while (lines.hasNext()) {
String line = (String) lines.next();
boolean selected = (ln == selection);
System.out.println(ln + (selected ? " * " : " : ") + line);
ln++;
}
}

private void warn (String msg) {
System.out.println("WARNING: " + msg);
}

public static void main (String[] args) {
try {
TextEditor editor = new TextEditor();
for (int i = 0; i < args.length; ) {
char op = args[i++].charAt(0);
System.out.println("Operation: " + op);
switch (op) {
case 'i':
editor.insertBefore(args[i++]);
break;
case 'a':
editor.insertAfter(args[i++]);
break;
case 'd':
editor.delete();
break;
case 'r':
editor.replace(args[i++]);
break;
case 's':
editor.select(Integer.parseInt(args[i++]));
break;
case 'f':
editor.find(args[i++]);
break;
case 'l': {
BufferedReader input =
new BufferedReader(
new InputStreamReader(
new FileInputStream(args[i++])));
editor.load(input);
input.close();
break;
}
case 'v': {
BufferedWriter output =
new BufferedWriter(
new OutputStreamWriter(
new FileOutputStream(args[i++])));
editor.save(output);
output.close();
break;
}
default:
System.out.println(" -- INVALID");
}
editor.display();
}
}
catch (IOException e) { System.out.println(e.getMessage()); }
}

}