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PostfixEvaluator - PostfixEvaluator.java Author...

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//******************************************************************* // PostfixEvaluator.java Author: Lewis/Loftus // // Solution to Programming Project 12.7 // // Evaluates a postfix expression that operates on integer operands // using the arithmetic operators +, -, *, /, and %. Inputs is // assumed to be in valid postfix form. //******************************************************************* / import java.util.Stack; import java.util.StringTokenizer; i public class PostfixEvaluator { p //---------------------------------------------------------------- // Parses the string and returns the int value. If the string is // invalid, return -1. //---------------------------------------------------------------- private static int getIntValue(String s) { int result = -1; try { result = Integer.parseInt(s); } catch (NumberFormatException e) {} return result; } //---------------------------------------------------------------- // Evaluates the postfix expression and returns the result //---------------------------------------------------------------- public static float evaluate(String expression) { Stack stack = new Stack(); StringTokenizer parser = new StringTokenizer(expression); String token; int tokenIntValue; float firstOperator, secondOperator; while (parser.hasMoreTokens()) { token = parser.nextToken(); char firstChar = token.charAt(0); if (Character.isDigit(firstChar) || // token is a positive or negative number (token.length() > 1 && firstChar == '-')) stack.push(new Float(getIntValue(token)));
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