Reading a text file and converting it to polynomials

Question

I currently have a text file:

3 5 6 9 3 4 6 7 2 3 5 7 2 5 3 

When reading in java, the file should display as 3x ^ 5 + 6x ^ 9. The second line will be read as 4x ^ 4 + 6x ^ 7 + 2. It is impossible to get my program to display this, because I do not know how to convert these numbers to this form . Currently, I only get numbers with spaces between them when I run the program.

Here is what I tried:

 import java.io.File; import java.io.FileNotFoundException; import java.util.Scanner; import javax.swing.JOptionPane; public class Driver { public static void main(String[] args) { try { @SuppressWarnings("resource") Scanner myfile = new Scanner(new File("poly.dat")); Polynomial[] mypolynomial; mypolynomial = new Polynomial[10]; int index = 0; if (myfile.hasNext() == true) { //ignore this part myfile.nextLine(); } else { System.out.println("Error: File is empty"); return; } while (myfile.hasNextLine()) { mypolynomial[index] = new Polynomial(myfile.nextLine()); index++; } String menu = "Please choose a Polynomial \n"; for (int i = 0; i < index; i++) { menu = menu + i + " " + mypolynomial[i].getNumber() + "\n"; } String choicemenu = "What do you want to do ? \n " + "A - Display a Polynomial \n " + "B - Add two Polynomial \n " + "C - Subtract two Polynoimal \n " + "D - Multiply two Polynomial \n "; String action = JOptionPane.showInputDialog(choicemenu); if (action.equals("A")) { int choice = Integer.parseInt(JOptionPane.showInputDialog(menu)); JOptionPane.showMessageDialog(null, mypolynomial[choice]); } } catch (FileNotFoundException e) { System.out.println(" OOOPS - something wrong - maybe the file name is wrong"); } } } public class Polynomial { //Testing the program String poly; public Polynomial(String p) { poly = p; } public String getNumber() { return poly; } public void setNumber(String p) { poly=p; } public String toString() { String result = "The Polynomial is " + poly; return result; } } 

I want to first display these numbers as polynomials, and then ultimately want to perform operations with them. Can anybody help me?

Answer 1

It seems that polynomials have values ​​that appear in pairs, i.e. 5 4 become 5x^4 . This means that you need to keep track of whether it is the first of the pair, the second pair or not a member of the pair. In the first case, you just need to print the value, but the second you need to have the value "x ^" +.

You can do the following in your constructor for the polyomial class:

• Create String polynomial = "" .

• Scroll the line traversed while tracking boolean isOnSecond .

• If !isOnSecond , add a value to read and set isOnSecond to true.

• Else isOnSecond == true add "x^" + value and set isOnSecond to false.

• Check if the line has a different value, and if it adds a "+" and saves the loop, otherwise it does nothing, because the line is completed.

This will give you lines that look like the result you want.

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Sample code inside your Polynomial constructor:

 public Polynomial(String p) { // First step is to create a scanner of the String // passed into the constructor. Scanner scanner = new Scanner(p); // Next step is to initialize the String poly // to an empty String so we can append to it. poly = ""; // Next we need to include a way of keeping track of // whether the value we just read was a first or second // member of a pair. We can do that with a boolean // initialized to false since the first use will be // when it is on the first of a pair. boolean isOnSecond = false; // Now we need to start looping through the values in // p which are separated by white space. Scanner has // a method for that, scanner.next(). while(scanner.hasNext()) { String currentValue = scanner.next(); // Now is where the boolean comes into play. if(isOnSecond) { // second of a pair // the second of a pair needs to have "x^" before its value poly = poly + "x^" + currentValue; // Here we need to check if there is another value coming after // and if there is append a " + " to poly if(scanner.hasNext() { poly = poly + " + "; } } else { // !isOnSecond, so is first of a pair // Only need to append the currentValue here poly = poly + currentValue; } isOnSecond = !isOnSecond; // toggles isOnSecond } }