Question

- Create a java class named SaveFile in which write the following:

Constructor: The class's constructor should take the name of a file as an argument

A method save (String line): This method should open the file defined by the constructor, save the string value of line at the end of the file, and then close the file.

- In the same package create a new Java class and it DisplayFile in which write the following:

Constructor: The class's constructor should take the name of a file as an argument

A method display(): This method should check if the file defined by the constructor  exist or not, if the file does not exist it displays the message "The file does not exists" and then exit the program, however if the file exists it displays the file contents line by line into the screen, and then close the file.

A method display (int n): This method is similar to display () but it displays the first n number of lines of the file's contents only. If the file contains less than n lines, it should display the file's entire contents.

A method display (int from, int to): This method is similar to display() but it displays the files's contents starting from line number from to the line number to. If the file contains less than to lines, it should display the file's contents. Note that, from is always less than to.

- In the same package, create another class called FilesDemo, in it's main method do the following:

create an instance of the class SaveFile to create new file named "lines.txt"

print the following lines into the file:

1-Lorem ipsum dolor sit amet

2-Consectetuer adipiscing elit

3-Sed diam nonummy nibh euismod tincidunt

4-Ut wisi enim ad minim veniam

5-Quis nostrud exerci tation ullamcorper

6-Suscipit lobortis nisl ut aliquip ex ea commodo consequat

7-Duis autem vel eum iriure dolor in hendrerit

8-Vel illum dolore eu feugiat nulla facilisis at vero eros

Create an instance of the class DisplayFile to open "lines.txt"

using this instance invoke the method display()

using this instance invoke the method display(3) and display(10)

using this instance invoke the method display(3, 5)

Run your program and make sure it prints the correct output.

Answer 1

SaveFile.java

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

public class SaveFile {
private String fileName;
  
public SaveFile(String fileName)
{
this.fileName = fileName;
}
  
public void save(String line)
{
FileWriter fw;
PrintWriter pw;
try {
// open the file in append mode
fw = new FileWriter(new File(this.fileName), true);
pw = new PrintWriter(fw);
pw.write(line + System.lineSeparator());
  
pw.flush();
fw.close();
pw.close();
} catch (IOException ex) {
System.out.println("Error in writing to file: " + this.fileName);
System.exit(-1);
}
}
}

DisplayFile.java

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class DisplayFile {
private String fileName;
  
public DisplayFile(String fileName)
{
this.fileName = fileName;
}
  
public void display()
{
Scanner fileReader;
try
{
fileReader = new Scanner(new File(this.fileName));
System.out.println("FILE CONTENTS LINE-BY-LINE:");
while(fileReader.hasNextLine())
{
System.out.println(fileReader.nextLine().trim());
}
System.out.println();
fileReader.close();
}catch(FileNotFoundException fnfe){
System.out.println("The file does not exist");
}
}
  
public void display(int n)
{
Scanner fileReader;
ArrayList<String> contents = new ArrayList<>();
try
{
fileReader = new Scanner(new File(this.fileName));
while(fileReader.hasNextLine())
{
contents.add(fileReader.nextLine().trim());
}
fileReader.close();
  
if(contents.size() < n)
{
System.out.println("ENTIRE FILE:");
for(String lines : contents)
{
System.out.println(lines);
}
System.out.println();
}
else
{
System.out.println("FIRST " + n + " LINES OF " + this.fileName + ":");
for(int i = 0; i < n; i++)
{
System.out.println(contents.get(i));
}
System.out.println();
}
}catch(FileNotFoundException fnfe){
System.out.println("The file does not exist");
}
}
  
public void display(int from, int to)
{
if(from > to)
System.out.println("From index should always be less than to index!\n");
else
{
Scanner fileReader;
ArrayList<String> contents = new ArrayList<>();
try
{
fileReader = new Scanner(new File(this.fileName));
while(fileReader.hasNextLine())
{
contents.add(fileReader.nextLine().trim());
}
fileReader.close();

if(contents.size() < to)
{
System.out.println("FILE CONTENTS FROM LINE " + from + ":");
for(int i = from; i < contents.size(); i++)
{
System.out.println(contents.get(i));
}
System.out.println();
}
else
{
System.out.println("FILE CONTENTS FROM LINE " + from + " TO " + to + ":");
for(int i = from; i <= to; i++)
{
System.out.println(contents.get(i - 1));
}
System.out.println();
}
}catch(FileNotFoundException fnfe){
System.out.println("The file does not exist");
}
}
}
}

FilesDemo.java

public class FilesDemo {
  
private static final String FILENAME = "lines.txt";
  
public static void main(String[] args)
{
SaveFile saveFile = new SaveFile(FILENAME);
saveFile.save("1-Lorem ipsum dolor sit amet");
saveFile.save("2-Consectetuer adipiscing elit");
saveFile.save("3-Sed diam nonummy nibh euismod tincidunt");
saveFile.save("4-Ut wisi enim ad minim veniam");
saveFile.save("5-Quis nostrud exerci tation ullamcorper");
saveFile.save("6-Suscipit lobortis nisl ut aliquip ex ea commodo consequat");
saveFile.save("7-Duis autem vel eum iriure dolor in hendrerit");
saveFile.save("8-Vel illum dolore eu feugiat nulla facilisis at vero eros");
  
DisplayFile displayFile = new DisplayFile(FILENAME);
displayFile.display();
displayFile.display(3);
displayFile.display(10);
displayFile.display(3, 5);
}
}

**************************************************************** SCREENSHOT ***********************************************************

lines.txt

CONSOLE OUTPUT :

SaveFile.java x DisplayFile.java x L Files Demo.java x lines.txt X Source History B.Q O PBRO 1-Lorem ipsum dolor sit amet 2-consectetuer adipiscing elit. 3-Sed diam nonummy nibh euismod tincidunt. 4-Ut wisi enim ad minim veniam 5-Quis nostrud exerci tation ullamcorpe. 6-Suscipit lobortis nisl ut aliquip ex ea commodo consequat 7-Duis autem vel eum iriure dolor in hendrerit 8-Vel illum dolore eu feugiat nulla facilisis at vero eros

run: FILE CONTENTS LINE-BY-LINE: 1-Lorem ipsum dolor sit amet 2-Consectetuer adipiscing elit 3-Sed diam nonummy nibh euismod tincidunt 4-Ut wisi enim ad minim veniam 5-Quis nostrud exerci tation ullamcorper 6-Suscipit lobortis nisl ut aliquip ex ea commodo consequat 7-Duis autem vel eum iriure dolor in hendrerit 8-Vel illum dolore eu feugiat nulla facilisis at vero eros FIRST 3 LINES OF lines.txt: 1-Lorem ipsum dolor sit amet 2-Consectetuer adipiscing elit 3-Sed diam nonummy nibh euismod tincidunt ENTIRE FILE: 1-Lorem ipsum dolor sit amet 2-Consectetuer adipiscing elit 3-Sed diam nonummy nibh euismod tincidunt 4-Ut wisi enim ad minim veniam 5-Quis nostrud exerci tation ullamcorper 6-Suscipit lobortis nisl ut aliquip ex ea commodo consequat 7-Duis autem vel eum iriure dolor in hendrerit 8-Vel illum dolore eu feugiat nulla facilisis at vero eros FILE CONTENTS FROM LINE 3 TO 5: 4-Ut wisi enim ad minim veniam 5-Quis nostrud exerci tation ullamcorper 6-Suscipit lobortis nisl ut aliquip ex ea commodo consequat BUILD SUCCESSFUL (total time: 0 seconds)