Welcome to the Java Programming Forums


The professional, friendly Java community. 21,500 members and growing!


The Java Programming Forums are a community of Java programmers from all around the World. Our members have a wide range of skills and they all have one thing in common: A passion to learn and code Java. We invite beginner Java programmers right through to Java professionals to post here and share your knowledge. Become a part of the community, help others, expand your knowledge of Java and enjoy talking with like minded people. Registration is quick and best of all free. We look forward to meeting you.


>> REGISTER NOW TO START POSTING


Members have full access to the forums. Advertisements are removed for registered users.

Results 1 to 5 of 5

Thread: Please help about data structures.

  1. #1
    Junior Member
    Join Date
    Sep 2012
    Posts
    7
    Thanks
    3
    Thanked 0 Times in 0 Posts

    Default Please help about data structures.

    Please help me, I got stuck on this one from yesterday til now. Long story short : I have to build an java apps for doing polynomial : addition, subtraction, derivative .... The data structure chosen is linked list. There are five classes

    Term class : hold the exponent and coefficient for each term of the polynomial

    Node class : each node have a term in it and a link to the next Node

    Orderedsequences class: contains the head of the ordered sequence, the term must be arranged from high exponent to low exponent. orderedsequence also contains a cursor to show the current term, and a count to show how many term in there.

    Polynomial class : contains method to manipulate polynomial : add term, subtract two polynomials, derivative...

    Test class: to test the method.


    Previously, when I use array as the data structure to hold the term, everything is fine, when I change to linked list lost of thing happen. I think I have a trouble with the insert method (insert new terms into orderedsequence) and isCurrent method in the Orderedsequence class. Please help.

    Here is the code for the five classes.

    public class Node
    {
    private Term data;
    private Node link;
     
    //constructor
     
    public Node(Term t,Node l)
    {
    data=t;
    link=l;
    }
     
    //add Node after this Node
    public void addNodeafter(Term item)
      {
      link =new Node (item,link);
      }
    //Accessor  
      public Term getTerm ()
      {
      return data;
      }
      public Node getLink(){
      return link;
      }
    //remove Node after this Node  
      public void removeNodeAfter()
      {
      link=link.link;
      }
    //Set the term for this Node
      public void setTerm (Term x)
      {
      data=x;
      }
    //Set the Link for this Node  
      public void setLink(Node x)
      {
      link=x;
      }
     
    //List copy
     
      public static Node listCopy(Node source)
      {
      Node ans=null;
      if(source != null)
      {
      ans=new Node (source.data,null);
      Node cursor=source.link;
      Node tail= ans;
      while(cursor != null)
      {
      tail.link = new Node (cursor.data,null);
      cursor = cursor.link;
      tail = tail.link;
      }
      }
      return ans;
     }
    }

    [CODE]
    public class Term implements Comparable<Term>
    {
      private double coeff;
      private int exp;  
     
      //constructor
      public Term (double x,int y)
      {
        coeff=x;
        exp=y;
     
      }
     
      // Return the value of the coefficient of this term
      public double getCoeff()
      {
        return coeff;
      }
     
      //Return the value of the power of this term
      public int getExp()
      {
        return exp;
      }
     
      //modify the coefficient of a term
      public void setCoeff(double d)
      {
        coeff = d;
      }
     
      //modify the coefficient of a term
      public void setExp(int i)
      {
        exp = i;
      }
     
      //this term and term a has the same power
      //Return a term that is a sum of this term and a
      public Term add(Term a)
      {
        return new Term(coeff+a.coeff,exp);
      }
     
      //this term and term a has the same power
      //Return a term that is a substraction of term a from this term
      public Term subtr(Term a)
      {
        return new Term(coeff-a.coeff,exp);
      }
     
      //Return the differnce of the two terms which has same power
     
      public Term subtract(Term t){
      return new Term(coeff-t.coeff,exp);
      }
     
      //Return a term that is a multiplication of this term and term a
      public Term mult(Term a)
      {
        return new Term(coeff*a.coeff,exp+a.exp);
      }
     
      //Return a term that is the derivative of this term
      public Term derivative()
      {
        return new Term (coeff*exp,exp-1);
      }
     
      //Return a term that is the integral of this term
      public Term integral()
      {
        return new Term(coeff/(exp+1),exp+1);
      }
     
      //Return the value of the definite integral from a to b of this term
     
      public double defintegral(double a,double b){
     
        return (integral().eval(b)-integral().eval(a));}
     
    //Compare the exponent of the two terms, return 0 if equals, -1 < , 1 >
      public int compareTo(Term t){
      int ans =0;
      if(exp>t.exp) ans = 1;
      else if (exp<t.exp) ans=-1;
      return ans;
      } 
     
      public boolean equals(Object obj)
      {
        boolean ans = false;
     
        if(obj instanceof Term && compareTo((Term)obj)==0&&coeff==((Term)obj).coeff) ans=true;
      return ans;
      }
     
      //Return value of this term at a particulate value
      public double eval(double x)
      {
        double ans=coeff*Math.pow(x,exp);
        return ans;
      }
     
      //Return a string that describes this term.
      public String toString()
      {
        String ans="";
        if(exp>1&&coeff!=0) ans=ans+coeff+"x^"+exp+" ";
        else if(exp==1&&coeff>1) ans=ans+coeff+"x";
        else if (exp==0&&coeff!=0) ans=ans+coeff;
        else if(exp==1&&coeff==1) ans=ans+"x";
        return ans;
      }
    }


    public class OrderedSequence implements Cloneable
    {
      private Node head;
      private int count;
      private Node cursor ;
     
      //Constructor with any length
     
      public OrderedSequence()
      {
        head=null;
        count=0;cursor=head;
      }
     
    //insert a term in the ordered sequence. Ordered from high exponent to low exponent.When the new term has same exponen
    //with an existing term, add the two together, if the result exponent is zero, remove the term.  
     
      public void insert(Term t)
      {
        if(head==null)
        {
        head=new Node(t,null);
        }
        else 
     
        {
          if(t.getExp()>head.getTerm().getExp())
        { 
          head=new Node (t,head);
          count++;
        }
        else
     
        {
        start();
        while (cursor != null&&t.getExp()!=cursor.getTerm().getExp())
        {
          advance();
        }
        if(cursor!=null)//the power of t is the same as one of the exp in the os
        {
        cursor.setTerm(new Term(t.getCoeff()+cursor.getTerm().getCoeff(),t.getExp()));
     
        count++;
     
        if(cursor.getTerm().getCoeff()==0) 
        {
          removeCurrent(); 
          count--;     
        }
     
        }
        else //cursor is null, there is no term in os has the same power as t
     
        {
        cursor.addNodeafter(t);count++;  
        } 
     
        }
        }
        } 
     
     
     
     //restart the cursor to the beginning position
      public void start()
      {
        cursor = head;
      }
     
     
    // return the number of terms in the array
      public int getCount(){
      return count;
      }
     
     
    //return the current position in the sequence
      public Term getCurrent()
      {
        return cursor.getTerm();
      }
     
      //check if cursor is in the current positions in this ordered sequence
      public boolean isCurrent()
      {
        boolean answer = false;
        if(cursor.getTerm()!=null)
          answer = true;
        return answer;
      }
     
      //move the cursor to the next term
      public void advance()
      {
     
        if(isCurrent() == true)
          cursor=cursor.getLink();
      }
     
     
      //remove the term at current 
      public boolean removeCurrent()
      {
        boolean ans=false;
        if(isCurrent() == true)
        {
          cursor.setTerm(cursor.getLink().getTerm());
          cursor.setLink(cursor.getLink().getLink());
          ans=true;
     
        }
        return ans;
      }
    //merge two ordered sequence together
      public OrderedSequence merge(OrderedSequence os){
     
        OrderedSequence ans=clone();start();
        while(cursor!=null)
        {
        ans.insert(os.getCurrent());
       advance();           
        }
      return ans;
      } 
     
      public OrderedSequence clone()
      {
      OrderedSequence ans= new OrderedSequence();
      start();
      while(cursor!=null)
      {
      ans.insert(getCurrent());  
      advance();
      }
      return ans;
      }
     
    /* public OrderedSequence clone(){
      OrderedSequence ans ;
      try 
      {
      ans=(OrderedSequence)super.clone();
      }
      catch (CloneNotSupportedException e)
      {
        throw new RuntimeException("This class does not implement Cloneable");
      }
      ans.head = head.clone();
      return ans;} */
     
    }


    public class Polynomial implements Cloneable
    {
      private OrderedSequence os;
     
      //Constructor
      public Polynomial()
      {
        os=new OrderedSequence();
      }
     
     
      public Polynomial (OrderedSequence ost)
      {
      os=ost;
      }
     
      //insert term with specified coefficient and exponent
     
      public void insert(double a,int b)
      {
      os.insert(new Term(a,b));
      }
     
      //get the degree of this polynomial
     
      public int getDegree()
      {
        os.start();
      return os.getCurrent().getExp();
      }
     
      public int numberOfTerms(){
      return os.getCount();
      }
     
      //Evaluate the value of a polynomial
     
      public double evaluate(double x)
      {
      double ans=0;os.start();
      while(os.isCurrent()==true)
      {
      ans=ans+os.getCurrent().eval(x);
      os.advance();
      }
      return ans;
      }
     
     
      //return the sum of this polynimial and polynomial t
      public Polynomial add(Polynomial t)
     {
     return new Polynomial(os.merge(t.os)); 
      }
     
     //return the difference between this polynomial and polynomial a
     public Polynomial sub(Polynomial a)
      {
      Polynomial ans=clone();
        a.os.start();
      while(a.os.isCurrent()==true)
      {
      ans.insert(-1*(a.os.getCurrent().getCoeff()),a.os.getCurrent().getExp());
      a.os.advance();
      }
      return ans;
      } 
     
      // Take derivative 
      public Polynomial derivative()
      {
      Polynomial ans=new Polynomial();
      os.start();
      while(os.isCurrent()==true)
      {
      ans.insert(os.getCurrent().derivative());os.advance();
      }
      return ans;
      }
     
      //Integrate polylinomial 
     
      public Polynomial integrate()
      {
      Polynomial ans=new Polynomial();
      os.start();
      while(os.isCurrent()==true)
      {
      ans.insert(os.getCurrent().integral());os.advance();
      }
      return ans;
      }
     
      //Definite integral from a to b
     
      public double definiteIntegral(double a,double b)
      {
      Polynomial inte=integrate();
      return (inte.evaluate(b)-inte.evaluate(a));
      }
     
      //Multiplication of this polynomial and polinomial a
     
      public Polynomial multiply(Polynomial a)
     
      {
      Polynomial ans =new Polynomial();
      os.start();
      while(os.isCurrent()==true)
      {
      a.os.start();
      while(a.os.isCurrent()==true)
      {
      ans.insert(os.getCurrent().mult(a.os.getCurrent()));
      a.os.advance();
      }
      os.advance();
      }
      return ans;
      }
     
      //Clone method for polynomial
      public Polynomial clone(){
      Polynomial ans=new Polynomial(os.clone()) ;
     
      return ans;}
     
      //Compares the whole term of this polynomial and polynomial a
      public boolean equals(Object obj)
      {
        boolean ans = false;
        if(obj instanceof Polynomial&&os.getCount() == ((Polynomial)obj).os.getCount())
        {
          os.start();((Polynomial)obj).os.start();
          while(os.isCurrent()==true&&os.getCurrent().equals(((Polynomial)obj).os.getCurrent())==true)
          {
          os.advance();((Polynomial)obj).os.advance();
          }
          if(os.isCurrent()==false) ans=true;
        }
        return ans;
      }
     
     
     
      //Insert a term into this polynomial
      public void insert (Term a)
      {
        os.insert(a);
      }
     
      //display the polynomial
      public String toString()
      {
        os.start();
        String ans="";
        while(os.isCurrent()==true)
        {
          ans=ans+os.getCurrent().toString();
          os.advance();
          if(os.isCurrent()==true&&os.getCurrent().getCoeff()!=0) ans=ans+" + "; 
        }
     
        return ans;
      }
    }

    public class TestLab2x{
      public static void main (String arg[]){
     
      //Make a new term 3.5x^4
     
      Term t1=new Term(2,4);
      Term tt=new Term(2,4);
      Term t2=new Term(2.5,4);
      Term t3=t1.add(t2);
      Term t4=new Term(1,1);Term t5=new Term(2,2);Term t6=new Term(3,3);Term t7=new Term(5,5);Term t8=new Term(10,0);
     
       System.out.println("This is the term t1 "+t1);
      //Compare term t1 and tt
     
      System.out.println("Compare t1 and tt "+t1.equals(tt));
      System.out.println("Compare t1 and t2 "+t1.equals(t2));
      System.out.println("Compare t1 and 1000 "+t1.equals(1000));
     
     //Extract the coefficient of t1
      System.out.println("The coefficient of t1 is "+t1.getCoeff());
     //Extract the exponent of t1
      System.out.println("The exponent of t1 is "+t1.getExp()); 
     
       System.out.println("This is the term t3 "+t3);
     
     //Extract the coefficient of t1
      System.out.println("The coefficient of t3 is "+t3.getCoeff());
     //Extract the exponent of t1
      System.out.println("The exponent of t3 is "+t3.getExp()); 
      //Derivative of a term
      Term t9=t1.derivative();System.out.println("Display t9 "+t9.toString());
      Term t10=t8.derivative();System.out.println("Display t10 "+t10.toString());
     
      //Evaluate t1 at x=2
      System.out.println("Value of t1 at x=2 is " + t1.eval(2));
     
       System.out.println("Display t8 "+t8.toString()+"\n");
     
       Polynomial p1=new Polynomial();
       p1.insert(t1);p1.insert(t5);
     
        System.out.println("Polynomial p1 is : " +p1.toString());
     
      }}
    Last edited by bruce88; September 16th, 2012 at 01:54 PM.


  2. #2
    Super Moderator Norm's Avatar
    Join Date
    May 2010
    Location
    Eastern Florida
    Posts
    18,633
    Thanks
    45
    Thanked 1,959 Times in 1,933 Posts

    Default Re: Please help about data structures.

    I think I have a trouble with the insert method (insert new terms into orderedsequence) and isCurrent method in the Orderedsequence class.
    Have you tried debugging the code by adding println statements to print out the values of variables as the code executes so you can see what the code is doing?

    Do you have print outs from the code that shows the problem? Can you post them and add comments to them that describes the problem and show what the output should be.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
    Junior Member
    Join Date
    Sep 2012
    Posts
    7
    Thanks
    3
    Thanked 0 Times in 0 Posts

    Default Re: Please help about data structures.

    This is what I got from running those codes:

    java.lang.NullPointerException
    at OrderedSequence.insert(OrderedSequence.java:56)
    at Polynomial.insert(Polynomial.java:149)
    at TestLab2x.main(TestLab2x.java:40)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Nativ e Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknow n Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Un known Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at edu.rice.cs.drjava.model.compiler.JavacCompiler.ru nCommand(JavacCompiler.java:272)

  4. #4
    Super Moderator Norm's Avatar
    Join Date
    May 2010
    Location
    Eastern Florida
    Posts
    18,633
    Thanks
    45
    Thanked 1,959 Times in 1,933 Posts

    Default Re: Please help about data structures.

    ava.lang.NullPointerException
    at OrderedSequence.insert(OrderedSequence.java:56)
    Look at line 56 and find the variable with the null value. Then backtrack in the code to see why that variable does not have a valid non-null value.

    The posted code is poorly formatted which makes it very hard to read and understand.
    For example:
      } 
     
        }
        }
        }
    }s should NOT be in a column. They should be inline vertically with the line with their pairing {
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
    Junior Member
    Join Date
    Sep 2012
    Posts
    7
    Thanks
    3
    Thanked 0 Times in 0 Posts

    Default Re: Please help about data structures.

    @Norm : thanks, I am trying to add the System.out.println to each section to see what is going on.

    Edit: I think I figure out the error. Thanks again Norm, your trick works.
    Last edited by bruce88; September 16th, 2012 at 04:56 PM.

Similar Threads

  1. [SOLVED] O(log n): a simple question for Logarithm in Data structures & Algo
    By chronoz13 in forum Algorithms & Recursion
    Replies: 1
    Last Post: September 7th, 2012, 08:20 AM
  2. [SOLVED] Data Structures: Symbolic Algebra with Trees
    By Staticity in forum What's Wrong With My Code?
    Replies: 2
    Last Post: August 20th, 2012, 01:42 AM
  3. Help with Loop Structures, If-else statement, and String
    By javabeg123 in forum Loops & Control Statements
    Replies: 2
    Last Post: December 6th, 2011, 09:01 PM
  4. Replies: 0
    Last Post: November 6th, 2011, 02:55 PM
  5. Data Structures(Binary Search Tree to AVL Tree)ASAP
    By jfAdik in forum Algorithms & Recursion
    Replies: 2
    Last Post: April 5th, 2010, 03:58 AM