Android Open Source - Calculator-for-Android Shunting Yard Parser

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License

The source code is released under:

Apache License

Java Source Code

//   Copyright 2012 Digipom Inc.
////from   w  w w.j  a  va 2s.c om
//   Licensed under the Apache License, Version 2.0 (the "License");
//   you may not use this file except in compliance with the License.
//   You may obtain a copy of the License at
//
//       http://www.apache.org/licenses/LICENSE-2.0
//
//   Unless required by applicable law or agreed to in writing, software
//   distributed under the License is distributed on an "AS IS" BASIS,
//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//   See the License for the specific language governing permissions and
//   limitations under the License.

package com.digipom.android.library.evaluator;

import java.util.ArrayList;
import java.util.EmptyStackException;
import java.util.List;
import java.util.Stack;

import com.digipom.android.library.evaluator.exception.ParseException;
import com.digipom.android.library.evaluator.lexer.Identifier;
import com.digipom.android.library.evaluator.lexer.Lexer;
import com.digipom.android.library.evaluator.lexer.NumberLiteral;
import com.digipom.android.library.evaluator.lexer.Operator;
import com.digipom.android.library.evaluator.lexer.Parenthesis;
import com.digipom.android.library.evaluator.lexer.PredefinedFunction;
import com.digipom.android.library.evaluator.lexer.Separator;
import com.digipom.android.library.evaluator.lexer.Token;
import com.digipom.android.library.evaluator.lexer.Operator.Associativity;

public class ShuntingYardParser {
  private final Lexer lexer;
  private final List<Token> outputList = new ArrayList<Token>();
  private final Stack<Token> stack = new Stack<Token>();

  private Token nextToken;

  ShuntingYardParser(String input, NumberPrecision numberPrecision) throws ParseException {
    this.lexer = new Lexer(input, numberPrecision);
    consume();
  }

  List<Token> parse() throws ParseException {
    while (nextToken != Token.EOF) {
      if (nextToken instanceof NumberLiteral || nextToken instanceof Identifier) {
        outputList.add(nextToken);
      } else if (nextToken instanceof PredefinedFunction || nextToken == Parenthesis.OPEN) {
        stack.push(nextToken);
      } else if (nextToken == Separator.COMMA) {
        try {
          popToLeftParenthesisToOutput();
        } catch (EmptyStackException e) {
          throw new ParseException("Misplaced comma or mis-matched parenthesis.");
        }
      } else if (nextToken instanceof Operator) {
        final Operator o1 = (Operator) nextToken;

        while (!stack.isEmpty() && stack.peek() instanceof Operator) {
          final Operator o2 = (Operator) stack.peek();

          if ((o1.associativity == Associativity.LEFT && o1.precedence <= o2.precedence)
           || (o1.associativity == Associativity.RIGHT && o1.precedence < o2.precedence)) {
            popStackTopToOutput();
          } else {
            break;
          }
        }

        stack.push(nextToken);
      } else if (nextToken == Parenthesis.CLOSE) {
        try {
          popToLeftParenthesisToOutput();
        } catch (EmptyStackException e) {
          throw new ParseException("Mis-matched parenthesis.");
        }

        // Pop the left parenthesis from the stack, but not to the
        // output queue.
        stack.pop();

        if (!stack.isEmpty() && stack.peek() instanceof PredefinedFunction) {
          popStackTopToOutput();
        }
      }

      consume();
    }

    while (!stack.isEmpty()) {
      if (stack.peek() instanceof Parenthesis) {
        throw new ParseException("Mis-matched parenthesis.");
      } else {
        popStackTopToOutput();
      }
    }

    return outputList;
  }

  private void popStackTopToOutput() {
    outputList.add(stack.pop());
  }

  private void popToLeftParenthesisToOutput() throws EmptyStackException {
    while (stack.peek() != Parenthesis.OPEN) {
      popStackTopToOutput();
    }

  }

  private void consume() throws ParseException {
    nextToken = lexer.nextToken();
  }
}

Java Source Code List

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