How to implement mathematical expression in Java?

Implementing a Simple Parser for arithmetic expressions in Java?

• So I'm confused about this project I have to do and need help (though I'm not too sure if anyone would understand this stuff). Here's what I have to do: "Implement a simple parser for arithmetic expressions in Java. The following is the context-free grammar for the arithmetic expressions. E->E+T | E-T | T T->T*F | T/F | F F->N | (E) | V Here N and V are nonterminals representing integers and variables. For simplicity, you may assume the possible values for integers in this project are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and the possible variable names are a, b, ..., z and A, B, ..., Y, Z. Extra credits for significantly more generality for either of the two parts. Requirements with hints 1. First, you need to remove left recursions for the above grammar, in order to write procedures. 2. For a given input arithmetic expression, you need to process it symbol by symbol, start it from the beginning, you can input the string incline, or use an array, whatever you feel easy. 3. The rule to write procedures is to use a function for each non-terminal, with the main( ) function corresponding to the start symbol. For each production rule, say A->BC, you can write procedure A as void funA( ) { funB( ); funC( ); } If a production rule has a terminal, say A-> BbC, you can write procedure A as void funA( ) { funB( ); match('b'); funC( ); } Here the function match(char x) is to check whether the input symbol is 'x'. This should be very important. 4. Your program must be supported by running results for at least 10 strikingly different expressions. 5. Do not forget documentations."

• Answer:

  You have been asked to implement this as a recursive descent parser. What you need to do is for a production rule like F-> N| (E) | V For this rule you will write: function F() { if(currToken.isDigit()) { //Add a digit to your parse tree else if(currToken.isParentheses()) { readNextToken(); E(); if(!currToken.isParentheses()) //Set error. etc. else readNextToken(); } else if(currToken.isVariable()) { //Add this to your parse tree. readNextToken(); } else //Set error etc. } If you don't need evaluation and just checking if it is a valid sentence in the language, then you don't need the parse tree stuff. Hope this helps.