Reading a text file in Java Classes

Problem:

Radio

- channels : Channel[] - volume : int

+ Radio(channels : Channel[], volume : int) + setChannels(channels : Channel[]) : void  + getChannels() : Channel[] + setVolume(volume : int) : void + getVolume() : int + saveChannelsToFile(filename : String) : void

Channel

- frequency : double  - name : String

+ Channel(frequency : double, name : String)  + setFrequency(frequency : double) : void  + getFrequency() : double  + setName(name : String) : void  + getName() : String  + toString() : String

You have to implement the previous two classes. The class Channel has two private variables, a constructor, setters and getters, and a toString mthod. The class Radio has an array of channels and a volume.

In the tester class, you are required to read input from a file called "channels.txt" using a Scanner. The first line in the input file is the number of channels. Each additional line in the input file represents the name of the channel and its frequency.

After reading the number of channels, you need to create an array of Channels and its length would be the number of channels.

For each additional line you read, you need to create a new channel and add it to the array.

After reading the input, you should create a new Radio object an give it the read channels array as a parameter. Then, you should call the method saveChannelsToFile(String filename) to save the channels array to a file called "radio.txt" using a Formatter. 

Output:

2

MixFM 104.4

RadioOne 105.5

MixFM 104.4

RadioOne 105.5 

Solution:

/**------------------------Channel.java---------------------*/
public class Channel {
 
 private double frequency;
 private String name;
 
 public Channel(double frequency, String name) {
  this.frequency = frequency;
  this.name = name;
 }

 public double getFrequency() {
  return frequency;
 }

 public void setFrequency(double frequency) {
  this.frequency = frequency;
 }

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }
}

/**------------------------Radio.java---------------------*/
import java.io.File;
import java.util.Formatter;

public class Radio {
 
 private Channel[] channels;
 private int volume;
 
 public Radio(Channel[] channels, int volume) {
  this.channels = channels;
  this.volume = volume;
 }

 public Channel[] getChannels() {
  return channels;
 }

 public void setChannels(Channel[] channels) {
  this.channels = channels;
 }

 public int getVolume() {
  return volume;
 }

 public void setVolume(int volume) {
  this.volume = volume;
 }
 
 public void saveChannelsToFile(String filename) {
 try {
 Formatter formatter = new Formatter(new File(filename));
   
 for (int i = 0; i < channels.length; i++) {
  formatter.format("%s\n", channels[i].getName()+
                           " "+channels[i].getFrequency(), true);
   }
   
   formatter.close();
  } catch (Exception e) {
   System.err.println("Could not save file");
  }
 }
}
/**------------------------RadioTester.java---------------------*/
import java.io.File;
import java.io.IOException;
import java.util.Scanner;

public class RadioTester {
 
 public static void main(String args[]) {
  Scanner scan;
  
 try {
 scan = new Scanner(new File("channels.txt"));
   
 int numberOfChannels = scan.nextInt();
   
 Channel[] channels = new Channel[numberOfChannels];
   
 for (int i = 0; i < numberOfChannels; i++) {
  String name = scan.next();
  double frequency = scan.nextDouble();
          channels[i] = new Channel(frequency, name);
   }
   
   scan.close();
   
   Radio radio = new Radio(channels, 10);
   radio.saveChannelsToFile("radio.txt");
   
  } catch (IOException e) {
   System.err.println("Error reading file");
  }
 }
}