problem solving using Linked List

[Mona Alsh]

Hi there!!
I'm trying to solve a Data Structure programming Exercise, here is the problem requirements:

Farey Fraction of level one is defined as sequence (0/1,1/1), at level two , it is (0/1,1/2,1/1), at level three is (0/1,1/3,1/2,2/3,1/1)
at level four (0/1,1/4,1/3,1/2,2/3,3/4,1/1). So that at each level n, a new fraction a+b/c+d is inserted between two neighbor fractions a/c and b/d only if c + d <= n. write a program which for a number n entered by the user extends the linked list(sequence of terms) at level n and then display them?

Here is my implementation, I think I'm following the right logic but I have some warnings regarding the Object type I'm passing to the add () method from the LinkedList class

Fraction Class:

import java.util.*;
public class Fraction
        {
        int Num ;
        int Den;

        public Fraction(int a, int b)
        {
        Num = a;
        Den = b;

        }

        public String toString()
        {
                 return Num + "/" + Den;
        }
}

FractionList class:

import java.util.*;
public class FractionList extends LinkedList
        {
        public FractionList(){
        super();
        }

        public void display()
        {
           for (int i = 0; i < size() ; i++)
                System.out.print(get(i));
        }

    }

and the sequence class which contains the methods to add fraction objects to the sequence and allow the user to enter the number of level
and define the method that should insert the fraction in the sequence between two adjacent terms if they meet the condition c + d <= n

import java.util.*;

public class FractionSequence
        {
        public static void main(String[] args)
        {

                FractionList fList = new FractionList();
                Fraction  t1,t2,t3;
                 t1 = new Fraction(1,1);
                 t2 = new Fraction(1,3);
                 t3 = new Fraction(2,3);
        try{
                fList.add(t1);
                fList.add(t2);
                fList.add(t3);
        }catch(IndexOutOfBoundException ex){}

                Scanner ab = new Scanner(System.in);
                int userInput;
                System.out.println("Please enter the number of terms to expand the sequence:");
                userInput = ab.nextInt();

                FractionList newList = insertFraction(fList,userInput);
                newList.display();

        }

        public static FractionList insertFraction(FractionList fL, int n)
        {       Fraction fNode1,fNode2;
                for (int i = 0; i< fL.size() ; i++)
                {
                fNode1 = (Fraction)fL.get(i);
                fNode2 = (Fraction) fL.get(i+1);

                if (fNode1.Den + fNode2.Den <= n)
                        {
                        int newNum = fNode1.Num + fNode2.Num;
                        int newDen = fNode1.Den + fNode2.Den;
                        Fraction newNode = new Fraction(newNum, newDen);
                        fL.add(i+1,newNode);
                        }
                }
                return fL;
        }
        }

I would really appreciate if you can help me find the error in my code !!

Thanks in advance

[Tony Docherty]

Welcome to the Ranch

I've edited your post by changing the 'javadoc' tags you used to 'code' tags so it displays properly on this forum.

[Greg Charles]

Hi Mona, welcome to JavaRanch!

It would be helpful if you posted the warnings you are getting. They probably are related to a new(ish) concept in Java called generics. Try changing the class declaration to:

public class FractionList extends LinkedList<Fraction>

and see if that makes them go away.

[Tony Docherty]

Your code contains IndexOutOfBoundException which should probably be IndexOutOfBoundsException

The warnings are due to you not using generics, see http://docs.oracle.com/javase/tutorial/extra/generics/index.html.
Note using generics is not compulsory (but is definitely recommended) and not using generics will not stop your code from running.

[Mona Alsh]

Tony Docherty wrote:Welcome to the Ranch

I've edited your post by changing the 'javadoc' tags you used to 'code' tags so it displays properly on this forum.

Thanks a lot ,, it is my first post !!

[Mona Alsh]

Greg Charles wrote:Hi Mona, welcome to JavaRanch!

It would be helpful if you posted the warnings you are getting. They probably are related to a new(ish) concept in Java called generics. Try changing the class declaration to:

public class FractionList extends LinkedList<Fraction>

and see if that makes them go away.

here is the warning :

FractionSequence.java:17: cannot find symbol
symbol : class IndexOutOfBoundException
location: class FractionSequence
}catch(IndexOutOfBoundException ex){}
^
Note: FractionSequence.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 error

[Mona Alsh]

Tony Docherty wrote:Your code contains IndexOutOfBoundException which should probably be IndexOutOfBoundsException

The warnings are due to you not using generics, see http://docs.oracle.com/javase/tutorial/extra/generics/index.html.
Note using generics is not compulsory (but is definitely recommended) and not using generics will not stop your code from running.

yes, it is something related to generics but I don't know how to fix it ,
I have tried casting the Fraction node to object and pass it to the add() method but didn't work either!!

[Greg Charles]

Actually, that first one is a compile error. The second one is a warning. The difference is that errors prevent you from getting .class files output from the compiler. Warnings mean the compiler isn't completely happy about it, but does compile your code into .class files.

In any case, Tony spotted the error and showed you how to fix it, and both of us guessed what the warning was, and I showed you how to fix that. You should be good to go, right?

[Carey Brown]

If you have

for( int i=0 ; i < list.size() ; i++ )
{
    Object a = list.get(i); // always works
    Object b = list.get(i+1); // will fail at end of list
}

[Mona Alsh]

Carey Brown wrote:If you have

for( int i=0 ; i < list.size() ; i++ )
{
    Object a = list.get(i); // always works
    Object b = list.get(i+1); // will fail at end of list
}

Thank you very much ,,
yah ,,, it didn't work , I'll use iterator instead !!

Thank you again for spotting this run-time error

[Mona Alsh]

I know it is a bit late,,,but I just had my holidays.
I don't know how to thank you, but you really helped me.
and here is my way giving back to this awesome community


Fraction Class

import java.util.*;
public class Fraction
        {
        int Num ;
        int Den;

        public Fraction(int a, int b)
        {
        Num = a;
        Den = b;

        }

        public String toString()
        {
                 return Num + "/" + Den + ",";
        }
}

FractionList class

import java.util.*;
public class FractionList extends LinkedList<Fraction>
        {
        public FractionList(){
        super();
        }

        public void display()
        {
           for (int i = 0; i < size() ; i++)
                System.out.print(get(i));
                System.out.println();
                }

    }

This the FractionSequence class

import java.io.*;
import java.util.*;

public class FractionSequence
	{
	public static void main(String[] args)
	{
		
		FractionList fList = new FractionList(); 
		Fraction  t1,t2,t3,t4,t5;
		 t1 = new Fraction(0,1);
		 t2 = new Fraction(1,1);
   		// t3 = new Fraction(1,2);
		// t4 = new Fraction(2,3);
		// t5 = new Fraction(1,1);
	try{		 
		fList.add(t1);
		fList.add(t2);
		//fList.add(t3);
		//fList.add(t4);
		//fList.add(t5);
	}catch(IndexOutOfBoundsException ex){}
	
		Scanner ab = new Scanner(System.in);
		int userInput;
	        System.out.print("The current sequence is ");
		fList.display();
		System.out.println("Please enter the number of terms to expand the sequence:");
                userInput = ab.nextInt();
		FractionList newList = fList;
		for(int i = 1; i <= userInput;i++)
		{
		newList = insertFraction(newList,i);
		}
		System.out.println("The list after expanding is:");
		newList.display();
		
	}

	public static FractionList insertFraction(FractionList fL, int n)
        {       Fraction fNode1,fNode2;
			int newSize = fL.size() - 1;   
                for ( int i = 0; i < newSize; i++)
                {
                fNode1 = (Fraction)fL.get(i);
                fNode2 = (Fraction) fL.get(i+1);

                if (fNode1.Den + fNode2.Den <= n)
                        {
                   	int newNum = fNode1.Num + fNode2.Num;
                   	int newDen = fNode1.Den + fNode2.Den;
                     	Fraction newNode = new Fraction(newNum, newDen);
                        fL.add(i+1,newNode);
			newSize++;  // increment newsize for the list to expand after adding terms 
                        }
                }
		return fL;

        }
	

	}

Thank you a lot