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Thread: Java calculator implementation

  1. #1
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    Default Java calculator implementation

    am basically attempting to create a calculator using a class hierarchy - the basic function will be:

    Convert the String representation into a list of Tokens
    Convert the List of Tokens into Polish Notation
    Calculate the result on the basis of Polish Notation
    I also need to represent objects -

    numbers operators and brackets.

    Following this i need to convert to polish notation - using a shunting yard algorithm and then compute the answer.

    I am ok with understanding the shunting yard but am unsure as to the class hierarchy part.

    The precedence is - Addition and Subtraction have a precedence of 2, and Multiplication and Division have a precedence of 3.

    I am assuming i need a filereader class and also classes to handle the different objects.

    I also need help in creating my own stacks and queues.

    Thanks


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    Default Re: Java calculator implementation

    There are two phases: Conversion from an Infix String to an RPN expression, and evaluation of the RPN expression. There is no theoretical reason why you couldn't do it all-in-one, but by having the intermediate RPN expression available, it would probably lead to more systematic debugging.



    For starters:

    For conversion to RPN, I would probably use a Stack<Character> object for the operator stack and a StringBuilder object for the output expression. Operator characters and operand numbers will be converted to Strings when you append them to the output expression.

    The conversion would use Stack methods push(), pop() and peek() and empty() and the StringBuilder append() method.


    For evaluation I would probably use a Stack<Double> object for the operand stack. Split the StringBuilder output expression into an array of Strings for processing, then step through the array. You will need Stack methods push(), pop() and empty(). You can index through the RPN array and see if the next item is a String corresponding to one of the operands.

    As you get into implementation details (on paper, before writing code) you may decide that certain functions or data structures can help keep it clean. A hashmap for operators' precedence might be handy (and cleaner) instead of hard-coding procedural precedence comparisons in the RPN conversion process, for example.


    Cheers!

    Z
    Last edited by Zaphod_b; November 4th, 2012 at 12:32 PM.

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    Default Re: Java calculator implementation

    Hi thanks for the help.

    How would I implement my own stack without using the java utils?

    also what sort of hierarchy should i use? I was thinking maybe a filereader class and then one to deal with the objects and then a main to tie it all together?

    thanks again

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    Default Re: Java calculator implementation

    so my thinking now is to have the following classes:

    stack class
    main - filereading, dealing with the numbers+operands
    shunting yard class

    Is this an acceptable sort of hierarchy?

    thanks

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    Default Re: Java calculator implementation

    Quote Originally Posted by why_always_me View Post
    so my thinking now is to have the following classes:

    stack class
    main - filereading, dealing with the numbers+operands
    shunting yard class

    Is this an acceptable sort of hierarchy?

    thanks
    Hi Guys my new thinking is :

    List class
    Node class
    Shunting yard class
    Main class
    Main includes the reverse Polich notation, filereader and tokenizer.

    My question now is how would i link main to the shunting yard? I was told I should create a list of objects which will be numbers, operands and brackets. Thanks again

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    Default Re: Java calculator implementation

    you can create instances of you class in your main. then you can use those instances to perform whatever you need to.
    i.e.

    ...main()
    {
    ShuntingYard var1;
    .....
    }

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