PDF (2) - Technische Universität München

Technische Universität München
Fakultät für Informatik
A. Berlea, M. Petter,
Dr. M. Schneider, P. Ziewer
WS 2004/2005
Lösungsvorschläge zu Blatt 11 (Fortsetzung)
20. Januar 2005
Übungen zu Einführung in die Informatik I
(Vorversion)
Aufgabe 31 Zeileneditor (Lösungsvorschlag)
d) Das Editormodell unter Einbeziehung eines Befehlsstacks könnte wie folgt aussehen:
java.io.BufferedReader
java.util.Vector
*
java.lang.StringBuffer
lines
stdin
Document
Ed
document
line, column: int
showDocument()
showLine()
showCursor()
userInputLoop()
getCommand()
getArgument()
main()
getLine()
getNumberOfLines()
getNumberOfColumns()
deleteLine()
insertLine()
insertTextInLine()
deleteCharacter()
store()
undo_stack
java.util.Stack
Command
*
+ undo()
InsertLineCommand
........
+ undo()
DeleteLineCommand
........
+ undo()
InsertTextInLineCommand
........
+ undo()
e) In der Klasse Ed muss nur die Befehlseingabe erweitert werden:
case ’u’:
if (document.undo())
showDocument();
else
System.out.println("No more undo.");
break;
Die erweiterte Klasse Document (mit internen Klassen):
import
import
import
import
java.io.BufferedReader;
java.io.BufferedWriter;
java.io.FileReader;
java.io.FileWriter;
.........
Lösung 11 (Fortsetzung)/ Seite 2
import java.io.IOException;
import java.util.Stack;
import java.util.Vector;
public class DocumentPlus {
private Vector lines;
private Stack undo_stack;
private String fileName;
public DocumentPlus(String file) throws IOException {
// init
lines = new Vector();
undo_stack = new Stack();
// read text from file
BufferedReader buffer = new BufferedReader(new FileReader(file));
String line;
while ((line = buffer.readLine()) != null) {
lines.add(new StringBuffer(line));
}
buffer.close();
fileName = file;
}
public boolean store() {
try {
BufferedWriter buffer = new BufferedWriter(new FileWriter(fileName));
for (int i = 0; i < lines.size(); i++) {
buffer.write(lines.get(i).toString());
buffer.newLine();
}
buffer.close();
return true;
} catch (IOException e) {
return false;
}
}
// getter
public String getLine(int line) {
try {
return lines.get(line - 1).toString();
} catch (ArrayIndexOutOfBoundsException e) {
return "";
}
}
public int getNumberOfLines() {
return lines.size();
}
public int getNumberOfColumns(int line) {
try {
Lösung 11 (Fortsetzung)/ Seite 3
return ((StringBuffer) lines.get(line - 1)).length();
} catch (ArrayIndexOutOfBoundsException e) {
return 0;
}
}
// public editing methods
public boolean deleteLine(int line) {
try {
undo_stack.push(new DeleteLineCommand(this, line));
} catch (Exception e) {
return false;
}
return true;
}
public boolean insertLine(int line, String text) {
try {
if (getNumberOfLines() == 0)
line = 1;
undo_stack.push(new InsertLineCommand(this, line, text));
} catch (Exception e) {
return false;
}
return true;
}
public boolean insertTextInLine(int line, int column, String text) {
try {
undo_stack.push(new InsertTextInLineCommand(this, line, column, text));
} catch (Exception e) {
return false;
}
return true;
}
public boolean deleteCharacter(int line, int column) {
try {
undo_stack.push(new DeleteCharacterCommand(this, line, column));
} catch (Exception e) {
return false;
}
return true;
}
// private editing methods
private void deleteLineInternal(int line) {
lines.remove(line - 1);
}
private void insertLineInternal(int line, String text) {
lines.add(line - 1, new StringBuffer(text));
}
Lösung 11 (Fortsetzung)/ Seite 4
private void insertTextInLineInternal(int line, int column, String text) {
((StringBuffer) lines.get(line - 1)).insert(column - 1, text);
}
private void deleteCharacterInternal(int line, int column) {
((StringBuffer) lines.get(line - 1)).deleteCharAt(column - 1);
}
// undo
public boolean undo() {
if (undo_stack.empty())
return false;
((Command) undo_stack.pop()).undo();
return true;
}
// internal command classes
abstract class Command {
DocumentPlus document;
Command(DocumentPlus document) {
this.document = document;
}
abstract void undo();
}
class InsertLineCommand extends Command {
int line;
InsertLineCommand(DocumentPlus document, int line, String text) {
super(document);
this.line = line;
document.insertLineInternal(line, text);
}
void undo() {
document.deleteLineInternal(line);
}
}
class DeleteLineCommand extends Command {
String text;
int line;
public DeleteLineCommand(DocumentPlus document, int line) {
super(document);
this.line = line;
this.text = document.getLine(line);
document.deleteLineInternal(line);
}
void undo() {
document.insertLineInternal(line, text);
Lösung 11 (Fortsetzung)/ Seite 5
}
}
class InsertTextInLineCommand extends Command {
int line, column, length;
InsertTextInLineCommand(DocumentPlus document, int line, int column, String text) {
super(document);
this.line = line;
this.column = column;
this.length = text.length();
document.insertTextInLineInternal(line, column, text);
}
void undo() {
for (int i = 0; i < length; i++)
document.deleteCharacterInternal(line, column);
}
}
class DeleteCharacterCommand extends Command {
int line, column;
char character;
DeleteCharacterCommand(DocumentPlus document, int line, int column) {
super(document);
this.line = line;
this.column = column;
this.character = document.getLine(line).charAt(column - 1);
document.deleteCharacterInternal(line, column);
}
void undo() {
document.insertTextInLineInternal(line, column, "" + character);
}
}
}