Editor.java

import java.util.Scanner;
import java.util.LinkedList;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;

public class Editor{
  LinkedList<String> list;
  int currentIndex = -1;
  boolean displayError = false;
  String lastErrorMessage = null;
  String fileName = null;

  public static void main(String[] args){
    // test append
    Editor ed = new Editor();
    ed.appendLines(new String[]{"hello", "world"});
    System.out.println("expect: world");
    System.out.println("   got: "+ed.getCurrentLine());

    System.out.println("expect: hello");
    System.out.println("   got: "+ed.getLine(1));

    System.out.println("expect: 1 hello");
    System.out.println("   got: "+ed.getCurrentLineWithNumber());

    ed.appendLines(new String[]{"hello", "world"});
    System.out.println("expect: 4");
    System.out.println("   got: "+ed.getLineCount());

    // test insert in the middle
    ed = new Editor();
    ed.appendLines(new String[]{"hello", "world"});
    ed.insertLines(new String[]{"hello1", "world1"});
    System.out.println("expect: world1");
    System.out.println("   got: "+ed.getCurrentLine());
    System.out.println("expect: hello");
    System.out.println("   got: "+ed.getLine(1));
    System.out.println("expect: hello1");
    System.out.println("   got: "+ed.getLine(2));
    System.out.println("expect: world1");
    System.out.println("   got: "+ed.getLine(3));
    System.out.println("expect: world");
    System.out.println("   got: "+ed.getLine(4));

    // test insert at the beginning
    ed = new Editor();
    ed.appendLines(new String[]{"hello", "world"});
    ed.getLine(1);
    ed.insertLines(new String[]{"hello1", "world1"});
    System.out.println("expect: world1");
    System.out.println("   got: "+ed.getCurrentLine());
    System.out.println("expect: hello1");
    System.out.println("   got: "+ed.getLine(1));
    System.out.println("expect: world1");
    System.out.println("   got: "+ed.getLine(2));
    System.out.println("expect: hello");
    System.out.println("   got: "+ed.getLine(3));
    System.out.println("expect: world");
    System.out.println("   got: "+ed.getLine(4));
    
    // test delete in the middle
    ed = new Editor();
    ed.appendLines(new String[]{"hello", "world", "again"});
    ed.deleteLine(2);
    System.out.println("expect: again");
    System.out.println("   got: "+ed.getCurrentLine());
    // test delete last
    ed.deleteLine(2);
    System.out.println("expect: hello");
    System.out.println("   got: "+ed.getCurrentLine());
    
    // test delete invalid line number
    ed = new Editor();
    ed.appendLines(new String[]{"hello", "world", "again"});
    System.out.println("expect: EditorException");
    try{
      ed.deleteLine(4);
    }catch (EditorException e){
      System.out.println("   got: EditorException");
    }
  }

  public Editor(){
    list = new LinkedList<String>();
  }

  public Editor(String fileName){
    list = new LinkedList<String>();
    try{
      Scanner scan = new Scanner(new File(fileName));
      this.fileName = fileName;
      while(scan.hasNext()){
        list.addLast(scan.nextLine());
        currentIndex++;
      }
    }catch(FileNotFoundException e){
      throw new EditorException(fileName+": No such file or directory");
    }
  }

  public String getCurrentLineWithNumber(){
    String result = getCurrentLine();
    int lineNumber = currentIndex+1;
    return lineNumber+" "+result;
  }

  public String getCurrentLine(){
    String result = null;
    if(0 <= currentIndex && currentIndex < list.size()){
      result = list.get(currentIndex);
    }else{
      lastErrorMessage = "invalid address";
      throw new EditorException(lastErrorMessage);
    }
    return result;
  }

  public String getLine(int lineNumber){
    String result;
    int index = lineNumber-1;
    if(isValidIndex(index)){
      currentIndex = index;
      result = getCurrentLine();
    }else{
      lastErrorMessage = "invalid address";
      throw new EditorException(lastErrorMessage);
    }
    return result;
  }

  private boolean isValidIndex(int index){
    return 0 <= index && index < list.size();
  }

  public void appendLines(String[] lines){
    if(lines.length == 0){
      return;
    }
    for(String line : lines){
      currentIndex++;
      list.add(currentIndex, line);
    }
  }
  
  public void insertLines(String[] lines){
    if(lines.length == 0){
      return;
    }
    if(currentIndex == -1){
      appendLines(lines);
    }else{
      currentIndex--;
      appendLines(lines);
    }
  }

  public void deleteCurrentLine(){
    list.remove(currentIndex);
    if(currentIndex > list.size()-1){
      currentIndex--;
    }
  }

  public void deleteLine(int num){
    int index = num-1;
    if(isValidIndex(index)){
      currentIndex = index;
      deleteCurrentLine();
    }else{
      lastErrorMessage = "invalid address";
      throw new EditorException(lastErrorMessage);
    }
  }

  public void writeOut(){
    if(fileName == null){
      lastErrorMessage = "no current filename";
      throw new EditorException(lastErrorMessage);
    }else{
      writeOutToFile(fileName);
    }
  }

  public void writeOutToFile(String fileName){
    try{
      PrintWriter writer = new PrintWriter(new File(fileName));
      Iterator<String> it = list.iterator();
      while(it.hasNext()){
        writer.println(it.next());
      }
    }catch (FileNotFoundException e){
    }
  }

  public int getLineCount(){
    return list.size();
  }

  public int charCount(){
    int result = 0;
    Iterator<String> it = list.iterator();
    while(it.hasNext()){
      result += it.next().length();
    }
    return result;
  }

  public int wordCount(){
    int result = 0;
    Iterator<String> it = list.iterator();
    while(it.hasNext()){
      String line = it.next();
      String[] words = line.split("\\s+");
      result += words.length;
    }
    return result;
  }

  public String toString(){
    return null;
  }
}