EvaluateDemonstration.java

import java.util.Stack; import java.util.Scanner; import java.util.regex.Pattern;

public class EvaluateDemonstration { public static void main(String[ ] args) { Scanner stdin = new Scanner(System.in); String expression; double answer; System.out.println("Please type an arithmetic expression made from"); System.out.println("unsigned numbers and the operations + - * /."); System.out.println("The expression must be fully parenthesized.");

do { System.out.print("Your expression: "); expression = stdin.nextLine( ); try { answer = evaluate(expression); System.out.println("The value is " + answer); } catch (Exception e) { System.out.println("Error." + e.toString( )); } } while (query(stdin, "Another string?"));

System.out.println("All numbers are interesting."); }

public static boolean query(Scanner input, String prompt) { String answer; System.out.print(prompt + " [Y or N]: "); answer = input.nextLine( ).toUpperCase( ); while (!answer.startsWith("Y") && !answer.startsWith("N")) { System.out.print("Invalid response. Please type Y or N: "); answer = input.nextLine( ).toUpperCase( ); }

return answer.startsWith("Y"); }

public static double evaluate(String s) // Precondition: The string is a fully parenthesized arithmetic expression // formed from non-negative numbers, parentheses, and the four operations // +, -, *, and /. // Postcondition: The string has been evaluated and the value returned. // Exceptions: Can throw an NumberFormatException if the expression contains // characters other than digits, operations, parentheses and whitespace. // Can throw IllegalArgumentException if the input line is an // illegal expression, such as unbalanced parentheses or a division by zero. { Scanner input = new Scanner(s); Stack numbers = new Stack( ); Stack operations = new Stack( ); String next; char first; while (input.hasNext( )) { if (input.hasNext(UNSIGNED_DOUBLE)) { next = input.findInLine(UNSIGNED_DOUBLE); numbers.push(new Double(next)); } else { next = input.findInLine(CHARACTER); first = next.charAt(0); switch (first) { case '+': // Addition case '-': // Subtraction case '*': // Multiplication case '/': // Division operations.push(first); break; case ')': // Right parenthesis evaluateStackTops(numbers, operations); break; case '(': // Left parenthesis break; default : // Illegal character throw new IllegalArgumentException("Illegal character"); } } } if (numbers.size( ) != 1) throw new IllegalArgumentException("Illegal input expression"); return numbers.pop( ); } public static void evaluateStackTops(Stack numbers, Stack operations) // Precondition: The top of the operations stack contains +, -, *, or /, and // the numbers stack contains at least two numbers. // Postcondition: The top two numbers have been popped from the numbers stack, and the // top operation has been popped from the operations stack. The two numbers have been // combined using the operation (with the second number popped as the left operand). // The result of the operation has then been pushed back onto the numbers stack. // Exceptions: Throws an IllegalArgumentException if the stacks are illegal or if the // operation results in a division by zero. { double operand1, operand2; // Check that the stacks have enough items, and get the two operands. if ((numbers.size( )

// These patterns are from Appendix B of Data Structures and Other Objects. // They may be used in hasNext and findInLine to read certain patterns // from a Scanner. public static final Pattern CHARACTER = Pattern.compile("\S.*?"); public static final Pattern UNSIGNED_DOUBLE = Pattern.compile("((\d+\.?\d*)|(\.\d+))([Ee][-+]?\d+)?.*?"); }

Based on the algorithm in EvaluateDemonstration.java from the textbook, write (in your report) the contents of both stacks after each character is evaluated in a fully parenthesized expression. You may write the stack values horizontally, as shown in the example below. An example analysis is provided below for the expression ( 6-9)/3): 6 5 0 6,9 15 15 15, 3 5 9 3