package bd;import java.util.Scanner;import java.util.Stack;public class Calculator { public static final String USAGE = "== usage ==\n" + "input the expressions, and then the program " + "will calculate them and show the result.\n" + "input 'bye' to exit.\n"; /** * @param args */ public static void main(String[] args) { String input = "(+ (- 12 2) (* 4 5))"; toPolishNotation(input); //toReversePolishNotation(input); /* System.out.println(USAGE); Scanner scanner = new Scanner(System.in); String input = ""; final String CLOSE_MARK = "bye"; System.out.println("input an expression:"); input = scanner.nextLine(); while (input.length() != 0 && !CLOSE_MARK.equals((input))) { System.out.print("Polish Notation (PN):"); try { toPolishNotation(input); } catch (NumberFormatException e) { System.out.println("\ninput error, not a number."); } catch (IllegalArgumentException e) { System.out.println("\ninput error:" + e.getMessage()); } catch (Exception e) { System.out.println("\ninput error, invalid expression."); } System.out.print("Reverse Polish Notation (RPN):"); try { toReversePolishNotation(input); } catch (NumberFormatException e) { System.out.println("\ninput error, not a number."); } catch (IllegalArgumentException e) { System.out.println("\ninput error:" + e.getMessage()); } catch (Exception e) { System.out.println("\ninput error, invalid expression."); } System.out.println("input a new expression:"); input = scanner.nextLine(); } */ System.out.println("program exits"); } /** * parse the expression , and calculate it. * @param input * @throws IllegalArgumentException * @throws NumberFormatException */ private static void toPolishNotation(String input) throws IllegalArgumentException, NumberFormatException { int len = input.length(); char c, tempChar; Stack< Character> s1 = new Stack< Character>(); Stack< Double> s2 = new Stack< Double>(); Stack< Object> expression = new Stack< Object>(); double number; int lastIndex = -1; for (int i=len-1; i>=0; --i) { c = input.charAt(i); if (Character.isDigit(c)) { lastIndex = readDoubleReverse(input, i); number = Double.parseDouble(input.substring(lastIndex, i+1)); s2.push(number); i = lastIndex; if ((int) number == number) expression.push((int) number); else expression.push(number); } else if (isOperator(c)) { while (!s1.isEmpty() && s1.peek() != ')' && priorityCompare(c, s1.peek()) < 0) { expression.push(s1.peek()); s2.push(calc(s2.pop(), s2.pop(), s1.pop())); } s1.push(c); } else if (c == ')') { s1.push(c); } else if (c == '(') { while ((tempChar=s1.pop()) != ')') { expression.push(tempChar); s2.push(calc(s2.pop(), s2.pop(), tempChar)); if (s1.isEmpty()) { throw new IllegalArgumentException( "bracket dosen't match, missing right bracket ')'."); } } } else if (c == ' ') { // ignore } else { throw new IllegalArgumentException( "wrong character '" + c + "'"); } } while (!s1.isEmpty()) { tempChar = s1.pop(); expression.push(tempChar); s2.push(calc(s2.pop(), s2.pop(), tempChar)); } while (!expression.isEmpty()) { System.out.print(expression.pop() + " "); } double result = s2.pop(); if (!s2.isEmpty()) throw new IllegalArgumentException("input is a wrong expression."); System.out.println(); if ((int) result == result) System.out.println("the result is " + (int) result); else System.out.println("the result is " + result); } /** * parse the expression, and calculate it. * @param input * @throws IllegalArgumentException * @throws NumberFormatException */ private static void toReversePolishNotation(String input) throws IllegalArgumentException, NumberFormatException { int len = input.length(); char c, tempChar; Stack< Character> s1 = new Stack< Character>(); Stack< Double> s2 = new Stack< Double>(); double number; int lastIndex = -1; for (int i=0; i< len; ++i) { c = input.charAt(i); if (Character.isDigit(c) || c == '.') { lastIndex = readDouble(input, i); number = Double.parseDouble(input.substring(i, lastIndex)); s2.push(number); i = lastIndex - 1; if ((int) number == number) System.out.print((int) number + " "); else System.out.print(number + " "); } else if (isOperator(c)) { while (!s1.isEmpty() && s1.peek() != '(' && priorityCompare(c, s1.peek()) <= 0) { System.out.print(s1.peek() + " "); double num1 = s2.pop(); double num2 = s2.pop(); s2.push(calc(num2, num1, s1.pop())); } s1.push(c); } else if (c == '(') { s1.push(c); } else if (c == ')') { while ((tempChar=s1.pop()) != '(') { System.out.print(tempChar + " "); double num1 = s2.pop(); double num2 = s2.pop(); s2.push(calc(num2, num1, tempChar)); if (s1.isEmpty()) { throw new IllegalArgumentException( "bracket dosen't match, missing left bracket '('."); } } } else if (c == ' ') { // ignore } else { throw new IllegalArgumentException( "wrong character '" + c + "'"); } } while (!s1.isEmpty()) { tempChar = s1.pop(); System.out.print(tempChar + " "); double num1 = s2.pop(); double num2 = s2.pop(); s2.push(calc(num2, num1, tempChar)); } double result = s2.pop(); if (!s2.isEmpty()) throw new IllegalArgumentException("input is a wrong expression."); System.out.println(); if ((int) result == result) System.out.println("the result is " + (int) result); else System.out.println("the result is " + result); } /** * calculate the two number with the operation. * @param num1 * @param num2 * @param op * @return * @throws IllegalArgumentException */ private static double calc(double num1, double num2, char op) throws IllegalArgumentException { switch (op) { case '+': return num1 + num2; case '-': return num1 - num2; case '*': return num1 * num2; case '/': if (num2 == 0) throw new IllegalArgumentException("divisor can't be 0."); return num1 / num2; default: return 0; // will never catch up here } } /** * compare the two operations' priority. * @param c * @param peek * @return */ private static int priorityCompare(char op1, char op2) { switch (op1) { case '+': case '-': return (op2 == '*' || op2 == '/' ? -1 : 0); case '*': case '/': return (op2 == '+' || op2 == '-' ? 1 : 0); } return 1; } /** * read the next number (reverse) * @param input * @param start * @return * @throws IllegalArgumentException */ private static int readDoubleReverse(String input, int start) throws IllegalArgumentException { int dotIndex = -1; char c; for (int i=start; i>=0; --i) { c = input.charAt(i); if (c == '.') { if (dotIndex != -1) throw new IllegalArgumentException( "there have more than 1 dots in the number."); else dotIndex = i; } else if (!Character.isDigit(c)) { return i + 1; } else if (i == 0) { return 0; } } throw new IllegalArgumentException("not a number."); } /** * read the next number * @param input * @param start * @return * @throws IllegalArgumentException */ private static int readDouble(String input, int start) throws IllegalArgumentException { int len = input.length(); int dotIndex = -1; char c; for (int i=start; i< len; ++i) { c = input.charAt(i); if (c == '.') { if (dotIndex != -1) throw new IllegalArgumentException( "there have more than 1 dots in the number."); else if (i == len - 1) throw new IllegalArgumentException( "not a number, dot can't be the last part of a number."); else dotIndex = i; } else if (!Character.isDigit(c)) { if (dotIndex == -1 || i - dotIndex > 1) return i; else throw new IllegalArgumentException( "not a number, dot can't be the last part of a number."); } else if (i == len - 1) { return len; } } throw new IllegalArgumentException("not a number."); } /** * return true if the character is an operator. * @param c * @return */ private static boolean isOperator(char c) { return (c=='+' || c=='-' || c=='*' || c=='/'); } }