20175316盛茂淞 2018-2019-2《Java程序設計》結對編程項目-四則運算 第一周 階段性總結
阿新 • • 發佈:2019-04-04
system system.in 出棧 bye ots 需求分析 tor 運算符 技術
20175316盛茂淞 2018-2019-2《Java程序設計》結對編程項目-四則運算 第一周 階段性總結
需求分析
- 自動生成四則運算題目(加、減、乘、除)。
- 既可以用前綴算法(波蘭算法)實現加減乘除也可以用後綴算法實現。
- 支持復合運算。
設計思路
- 首先我們先實現前綴表達式的方法,通過閱讀材料大致了解到如下方法:
- 前綴表達式的計算機求值:
從右至左掃描表達式,遇到數字時,將數字壓入堆棧,遇到運算符時,彈出棧頂的兩個數,用運算符對它們做相應的計算(棧頂元素 op 次頂元素),並將結果入棧;重復上述過程直到表達式最左端,最後運算得出的值即為表達式的結果。
例如前綴表達式“- × + 3 4 5 6”:
(1) 從右至左掃描,將6、5、4、3壓入堆棧;
(2) 遇到+運算符,因此彈出3和4(3為棧頂元素,4為次頂元素,註意與後綴表達式做比較),計算出3+4的值,得7,再將7入棧;
(3) 接下來是×運算符,因此彈出7和5,計算出7×5=35,將35入棧;
(4) 最後是-運算符,計算出35-6的值,即29,由此得出最終結果。
可以看出,用計算機計算前綴表達式的值是很容易的。
- 隨後後綴表達式實現方法上與前綴有異同之處:
- 後綴表達式的計算機求值:
與前綴表達式類似,只是順序是從左至右:
從左至右掃描表達式,遇到數字時,將數字壓入堆棧,遇到運算符時,彈出棧頂的兩個數,用運算符對它們做相應的計算(次頂元素 op 棧頂元素),並將結果入棧;重復上述過程直到表達式最右端,最後運算得出的值即為表達式的結果。
(1) 從左至右掃描,將3和4壓入堆棧;
(2) 遇到+運算符,因此彈出4和3(4為棧頂元素,3為次頂元素,註意與前綴表達式做比較),計算出3+4的值,得7,再將7入棧;
(3) 將5入棧;
(4) 接下來是×運算符,因此彈出5和7,計算出7×5=35,將35入棧;
(5) 將6入棧;
(6) 最後是-運算符,計算出35-6的值,即29,由此得出最終結果。
代碼
import java.util.Scanner; import java.util.Stack; public class sizeyunsuan { 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) { 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=='/'); } }
測試說明
- 正常測試
- 異常測試
- 邊界測試
碼雲鏈接
[碼雲連接]https://gitee.com/shengmaosong/java-besti-20175316/blob/master/jiedui/jiedui1/sizeyunsuan.java
UML圖
## 參考資料
- 逆波蘭算法
- 前綴解析
- IDEA上傳至碼雲
結對學習照片
20175316盛茂淞 2018-2019-2《Java程序設計》結對編程項目-四則運算 第一周 階段性總結