Help with this problem please

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 O.
//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 followina 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 In 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());}
}
}