Question

I need help understanding this programming assignment. I do not understand it at all. Someone provided me with the code but when I run the code on eclipse it gives an error. Please explain this assignment to me please.

Write a simple line editor. Keep the entire text in an ArrayList object, one line in a separate index position. Start the program by entering the EDIT file, after which a prompt appears along with the line number. If the letter I is entered with a number n following it, then insert the text to be followed on line n. If I is not followed by a number, then insert the text on the current line. If D is entered with two numbers n and m, one n, or no number following it, then delete lines n through m, line n, or the current line. Do the same with the command L, which stands for listing lines. If A is entered, then append the text to the existing lines. Entry E signifies exit and saving the text in a file. Note: If you prefer, you can use a LinkedList object instead of ArrayList. Sample of the input and output: EDIT textin.txt 1> The first line 2> 3> And another line 4> I 3 3> The second line 4> One more line 5> L 1> The first line 2> 3> The second line 4> One more line 5> And another line 5> D2 4> L 1> The first line 2> The second line 3> One more line 4> And another line 5>E //This is now line 5, not 3; 1/ line 5, since L was issued from line 5; // line 4, since one line was deleted; //this and the following line was deleted; // now have new number;

Here is the code:

• import java.io.BufferedReader;

  import java.io.File;

  import java.io.FileReader;

  import java.io.IOException;

  import java.util.ArrayList;

  import java.util.List;

  import java.util.Scanner;

  public class TextEditor {

  public static List<String> lines = new ArrayList<String>();

  public static void main(String[] args) throws IOException

  {

  Scanner s = new Scanner(System.in);

  System.out.print("Input file: ");

  String fileName = s.nextLine();

  BufferedReader br = new BufferedReader(new FileReader(new File(fileName)));

  String str="";

  int count=0;

  while((str=br.readLine())!=null)

  {

  lines.add(count, str);

  System.out.println((++count) + "> "+ str);

  }

  String text="";

  String command = "";

  System.out.print((++count)+"> ");

  command=s.nextLine();

  String commandArr[];

  int flag;

  while(!command.equals("E"))

  {

  flag=0;

  commandArr = command.split("\\s");

  if(commandArr[0].equals("I")) //Insertion

  {

  while(true)

  {

  if(commandArr.length==1&&flag!=2)

  {

  System.out.print((count)+"> ");

  text = s.nextLine();

  insertLine(text,count-1);

  }

  else if(commandArr.length==2&&flag!=2)

  {

  System.out.print((commandArr[1])+"> ");

  count=Integer.parseInt(commandArr[1]);

  text = s.nextLine();

  insertLine(text,Integer.parseInt(commandArr[1])-1);

  }

  else

  insertLine(text,count-1);

  System.out.print((++count)+"> ");

  command=s.nextLine();

  commandArr = command.split("\\s");

  if(commandArr[0].equals("I")||commandArr[0].equals("L")||commandArr[0].equals("D")||commandArr[0].equals("E"))

  {

  flag=1;

  break;

  }

  else

  {

  flag=2;

  text=command;

  }

  }

  }

  else if(commandArr[0].equals("L")) //Listing

  {

  printList();

  }

  else if(commandArr[0].equals("D")) //Deletion

  {

  if(commandArr.length==1)

  {

  deleteLine(count-1,count-1);

  }

  else if(commandArr.length==2)

  {

  deleteLine(Integer.parseInt(commandArr[1])-1,Integer.parseInt(commandArr[1])-1);

  }

  else if(commandArr.length==3)

  {

  deleteLine(Integer.parseInt(commandArr[1])-1,Integer.parseInt(commandArr[2])-1);

  }

  count=lines.size();

  }

  if(flag!=1)

  {

  System.out.print((count++)+"> ");

  command = s.nextLine();

  }

  }

  }

  public static void insertLine(String text,int count)

  {

  lines.add(count,text);

  }

  public static void deleteLine(int start,int end)

  {

  for(int i=start;i<=end;i++)

  lines.remove(i);

  }

  public static void printList()

  {

  for(int i=0;i<lines.size();i++)

  System.out.println((i+1)+"> "+lines.get(i));

  }

  }

Answer 1

Please find Below corrected code. This should work. But before you run the code. let me tell you whats going on and whats this assignment is all about. I will make my level best to make you understand the problem.

Lets understand the ques.

We have to create a text editor in which we can edit text. just like vim or emacs or notepad etc

There are 3 main operation that should be present (in notepad there are several and notepad++ many more)

1. Insert at following line at line number specified. eg  I 3 will insert at line 3
2. Delete the lien at number specified e.g D 3 will delete line 3
3. Display the text editor content eg. L

Now lets understand the execution of program

1. Initially when program runs it read the file you provided and print it as is; (students.txt has 3 lines and 2nd line empty)

Input file: students.txt
1> The f lne
2>
3> and another lne
4>

'2. Now the program ask the user what operation do you want to perform on your text. Let's say we want to insert newer lines in our text at line 3. Hence, the line at 3 will shift down

4> I 3
3> second
4> new

3. Now the two new lines have been added at line 3. Now if we want to see how our text now looks like we Display with L

5> L
1> The f lne
2>
3> second
4> new
5> and another lne

4. If you notice "and another lne" is now shifted down as we inserted two lined at 3

5. Now lets say we want to delete line 2 which is empty we give command D 2

5> D 2

6. Now the line at 2 has been deleted.

7. But we cant see it. To do that we command Display L to display our text now.

4> L
1> The f lne
2> second
3> new
4> and another lne

8. We can see empty line gone and all other line has move upward.

9. Next we are done and want to exit we command E

and thats done!!. You can now run the below program.

 import java.io.BufferedReader; import java.io.File; import java.io.FileReader; import java.io.IOException; import java.util.ArrayList; import java.util.List; import java.util.Scanner; public class TextEditor { public static List < String > lines = new ArrayList < String > (); public static void main(String[] args) throws IOException { Scanner s = new Scanner(System.in); System.out.print("Input file: "); String fileName = s.nextLine(); BufferedReader br = new BufferedReader(new FileReader(new File(fileName))); String str = ""; int count = 0; while ((str = br.readLine()) != null) { lines.add(count, str); System.out.println((++count) + "> " + str); } String text = ""; String command = ""; System.out.print((++count) + "> "); command = s.nextLine(); String commandArr[]; int flag; while (!command.equals("E")) { flag = 0; commandArr = command.split("\\s"); if (commandArr[0].equals("I")) //Insertion { while (true) { if (commandArr.length == 1 && flag != 2) { System.out.print((count) + "> "); text = s.nextLine(); insertLine(text, count - 1); } else if (commandArr.length == 2 && flag != 2) { System.out.print((commandArr[1]) + "> "); count = Integer.parseInt(commandArr[1]); text = s.nextLine(); insertLine(text, Integer.parseInt(commandArr[1]) - 1); } else insertLine(text, count - 1); System.out.print((++count) + "> "); command = s.nextLine(); commandArr = command.split("\\s"); if (commandArr[0].equals("I") || commandArr[0].equals("L") || commandArr[0].equals("D") || commandArr[0].equals("E")) { flag = 1; break; } else { flag = 2; text = command; } } } else if (commandArr[0].equals("L")) //Listing { printList(); } else if (commandArr[0].equals("D")) //Deletion { if (commandArr.length == 1) { deleteLine(count - 1, count - 1); } else if (commandArr.length == 2) { deleteLine(Integer.parseInt(commandArr[1]) - 1, Integer.parseInt(commandArr[1]) - 1); } else if (commandArr.length == 3) { deleteLine(Integer.parseInt(commandArr[1]) - 1, Integer.parseInt(commandArr[2]) - 1); } count = lines.size(); } if (flag != 1) { System.out.print((count++) + "> "); command = s.nextLine(); } } } public static void insertLine(String text, int count) { lines.add(count, text); } public static void deleteLine(int start, int end) { for (int i = start; i <= end; i++) lines.remove(i); } public static void printList() { for (int i = 0; i < lines.size(); i++) System.out.println((i + 1) + "> " + lines.get(i)); } }