TextFileWithComments

public class TextFileOperations {

    public static void main(String[] args){
        //creating a ReadFile object to execute methods on it
        ReadFile rf = new ReadFile();

        //method openFile() from ReadFile.java
        //opens the current file "Input.txt" from the project directory
        rf.openFile();

        //method redWriteFile() from ReadFile.java
        //reads lines from "Input.txt"
        //writes sorted lines to "Output.txt"
        rf.readWriteFile();

        //method closeFile() from ReadFile.java
        //closes the used resources
        rf.closeFile();
    }
}

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import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Formatter;
import java.util.List;
import java.util.Scanner;

public class ReadFile{

    private Scanner scan;

    //openFile() checks if there is a file named "Input.txt"
    // and if there is - opens it  from the project directory
    public void openFile(){
        try{
                scan = new Scanner(new File("Input.txt"));
        }
        catch(FileNotFoundException ex){
                System.err.println("File not found!");
        }
    }

   //the most important method in the program
    //reads from file
    //sorts the product prices
    //writes to new file
    public void readWriteFile(){

        //two lists to hold each product's name and price
        List<Double> priceList = new ArrayList<Double>();
        List<String> productList = new ArrayList<String>();
        String product = "";
        Formatter formatter = null;
        DecimalFormat df = new DecimalFormat("#.00");

        //a Product object which is used as a temporary object to holf info
        Product currentProduct = new Product();

        //executes while the scanner reaches the end of the file
        //every line is in the format
        //[productName] [productPrice]
        while(scan.hasNext()){
            product = scan.next();
            double price = Double.parseDouble(scan.next());
            priceList.add(price);
            productList.add(product);

            //as the program is using Lists and not Arrays, we are unnable to use
            //Arrays.sort(arrayName)
            Collections.sort(priceList);
        }

        //this is unnecesary step, it is only used for your comfort, thus you are
        //able to see what is going on with the products - in the console
        for (int i = 0; i < priceList.size(); i++) {
            System.out.printf("%s %s\n", df.format(priceList.get(i)), productList.get(i));
        }
        try{
            formatter = new Formatter("Output.txt");
            for (int i = 0; i < priceList.size(); i++) {

                //setting name and price for each product from the above two lists
                currentProduct.setProductName(productList.get(i));
                currentProduct.setProductPrice(df.format(priceList.get(i)));

                //writing the new product info in the newly created file "Output.txt"
                formatter.format("%s %s\r\n", currentProduct.getProductPrice(), currentProduct.getProductName());
            }
        }
        catch(IOException ioex){
                System.err.println("IO Exception occured.");
        }

        //closing the used resources from Formatter class
        finally{
                formatter.close();
        }
    }

    public void closeFile(){

        //closing the used resources from Scanner class
        scan.close();
    }
}

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public class Product{
    private String productName;
    private String productPrice;

    //generating product name and product price getters and setters
    public String getProductName() {
        return productName;
    }

    public void setProductName(String productName) {
        if (productName == null) {
            throw new IllegalArgumentException("Illegal argument exception.");
        }
        this.productName = productName;
    }

    public String getProductPrice() {
        return productPrice;
    }

    public void setProductPrice(String string) {
        this.productPrice = string;
    }
}