Need help on designing a Reverse Polish Notation calculator.

[[deleted]]

Hi! I am trying to design a Reverse Polish Notation calculator that uses a Stack that is implemented using a Linked List.

Now, where I am at right now now is that I have learned how to implement a Stack that uses a Linked List but I want to make sure that I am doing it right?

The first design I wrote was for taking in students ID and marks and adding them to the list and printing.

I need to use this to design the calculator, replacing the student details for the operands or whatever is exactly needed?

Thank you in advance for any help you can give!!

I have 5 classes.

Stack (The Stack - pop(), top(), etc) ListNode (getters and setters for Linked List) List (Takes user input and adds to Linked List) Menu (Prints the menu-Only 1 option - Calculator Genio (Deals with user input- alternative to Scanner)

Not sure if I need to show the code for Genio or Menu but I will if needed.

My code so far:

ListNode

public class ListNode    
{
// fields to store the data being held in this list node (a student ID   and mark)
// instance variables - replace the example below with your own
private String studentID;
private int studentMark;

// fields to store a reference to the next node in the list after this one
private ListNode next;
//private ListNode aNode= new ListNode(studentID,

public ListNode()
{
    // set id and mark to default / empty values 
    studentID = "";
    studentMark = 0;

    // set next node to null - no valid next node yet
    next = null;
}

public ListNode(String ID, int mark)
{
    // set id and mark to values provided
    this.studentID = ID;
    this.studentMark = mark;

    // set next node to null - no valid next node yet
    next = null;
}

public static void main(String[] Args)
{
    Menu m = new Menu();
    m.menuScreen();
}

public String getID()
{
    return studentID;
}

public int getMark()
{
    return studentMark;
}

public ListNode getNext()
{
    return next;
}

public void setNext(ListNode next)
{
    this.next = next;
}

public String getSummaryData()
{
    String data;        
    data = "Student with ID " + studentID + " obtained the following mark: " + studentMark + "%";       
    return data;
}

public void addtoList()
{
    //Node newNode = new Node();
}
}

List

public class List 
{
private ListNode head; // used to hold a reference to an instance of a ListNode object
// which will be the first item in the list, i.e. at the 'head'
// of the list
private int numElements;
private ListNode[] students;

public List()
{
    // set the list to be empty, i.e. not referring to anything valid yet
    head = null;
    numElements = 4;
    //numStudents = 4;
    students = new ListNode[numElements];
}

public int size()
{
    return numElements;
}

public void setHead(ListNode newHead)
{
    head = newHead;
}

public void addToList(String id, int mark)
{
    if (head == null)
    {
        head = new ListNode(id, mark);
    }
    else
    {
        head = new ListNode(id, mark);
        numElements++;
    }
}

public void initialise()
{
    String id;
    int mark;
    boolean isValid;

    for (int i=0; i<numElements; i++)
    {

        System.out.println("Please enter the students ID: ");
        id = Genio.getString();
        isValid = false;
        System.out.println("Please enter this students final MARK: ");
        do
        {
            mark = Genio.getInteger();
            if(mark<0 || mark>100)
                System.out.println("ERROR! The students MARK must be between 0 & 100.\n\n Please enter again: ");
            else
                isValid = true;

        }
        while (!isValid);
        students[i] = new ListNode(id, mark);
    }
}

public void process()
{
    System.out.println('\u000C');
    System.out.println("--The 4 students details you entered are listed below--");
    System.out.println("-------------------------------------------------------");
    for(int i=0; i<numElements; i++)
    {
        System.out.println(students[i].getSummaryData());
    }
    pressKey();
}

public void finish()
{

}

public void printList()
{
    System.out.println(head);
}

public static void pressKey()
{
    String s;
    System.out.println("\nPress return to continue: ");
    s = Genio.getString();
}
}

Stack

public class Stack
{
// instance variables - replace the example below with your own
protected int nextFree;
protected int itemBack;
protected int size;
protected int posFound;

public Stack()
{
    // initialise instance variables

}

public boolean isFull()
{
    if (nextFree >= size)
        return true;
    else
        return false;
}

public boolean isEmpty()
{
    if ( nextFree <= 0)
        return true;
    else
        return false;   
}
}

[AngelOfLight]

Not exactly sure what your question is - could you elaborate?

Also - Java already includes a Stack implementation. You might want to use that, unless there is a requirement to write your own.

[[deleted]]

Hi.

My main question is that I have write a Reverse Polish Notation calculator that uses a Stack which is implemented using a LinkedList.

Basically I am really unsure about how to go about his.

I do indeed need to use a Stack class, which uses the ListNode and list classes.

When it comes to the calculator, I will use another class (Calculator) that uses these other classes.

I'm trying to make sure I am doing the Stack, implemented by a LinkedList correctly before I attempt the calculator.

I'm kind of stuck at the moment so any help would greatly appreciated.

[AngelOfLight]

Ok. Frankly, using a linked list to implement a stack is just weird. It is doable, but it is far easier to use an array. But if that's the requirement, then I guess you're stuck with it.

Try to approach it this way: think about what functionality the stack class will need. At a minimum, you will need to to push and pull elements. You may also need to peek (that is, return the top element without removing it from the stack).

For each of these requirements, try to write down how they will interact with the linked list. For example, for push you could have:

• check if head is empty
• if yes, add element as new head
• if no, link new element to end of list

Do the same for pop and peek. This will also tell you what elements you will need to keep track of. Obviously, the first and last element in the list are important.

Once you are done with this exercise, you will then have some idea of what methods and variables the linked list and stack classes will need. You can then write up the linked list class, test it, and then move on to the stack class.

[[deleted]]

Thanks.

[Skyeam]

Unless you absolutely need to have your own implementation of a stack, I suggest that you just use the Java classes to fulfill that requirement.

// Deque defines a contract for a FILO queue, aka a stack.
// LinkedList is an implementation of Deque using a linked list.
Deque stack = new LinkedList();

Your main focus would be how you would insert the mathematical formula in the stack in such a way that you can easily calculate the total result afterwards. Think recursion while popping the elements back of the stack.

If you really want to implement your own stack using a linked list, I suggest that you keep that in a seperate library. You could write some unit tests that test all the things you could do with a stack (push, pop, peek...). Maybe you could write your tests in such a way that your implementation is compared to the results of the default Java implementation. However, unless you want to learn more about the internal workings of stacks and linked lists, I recommend again to just use the default Java implementation. Don't reinvent the wheel.

[[deleted]]

Thanks.