20155237 第十一週java課堂程序

20155237 第十一週java課堂程序

內容一：後綴表達式

abcde/-f+

內容二：實現Linux下dc的功能，計算後綴表達式的值

填充下列代碼：

import java.util.Scanner;

           public class MyDCTester  {

            public static void main (String[] args) {

            String expression, again;

             int result;

             try
             {
                   Scanner in = new Scanner(System.in);

                   do
                       {
                         MyDC evaluator = new MyDC();
                         System.out.println ("Enter a valid postfix expression: ");
                         expression = in.nextLine();

                         result = evaluator.evaluate (expression);
                         System.out.println();
                         System.out.println ("That expression equals " + result);

                         System.out.print ("Evaluate another expression [Y/N]? ");
                         again = in.nextLine();
                         System.out.println();
                       }
                   while (again.equalsIgnoreCase("y"));
             }
             catch (Exception IOException)
             {
                   System.out.println("Input exception reported");
                 }
           }
  }
  import java.util.StringTokenizer;
   import java.util.Stack;
           public class MyDC
  {
             /** constant for addition symbol */
             private final char ADD = '+';
           /** constant for subtraction symbol */
           private final char SUBTRACT = '-';
           /** constant for multiplication symbol */
           private final char MULTIPLY = '*';
           /** constant for division symbol */
           private final char DIVIDE = '/';
           /** the stack */
           private Stack<Integer> stack;

           public MyDC() {
             stack = new Stack<Integer>();
           }

           public int evaluate (String expr)
           {
             int op1, op2, result = 0;
             String token;
             StringTokenizer tokenizer = new StringTokenizer (expr);

             while (tokenizer.hasMoreTokens())
             {
               token = tokenizer.nextToken();

              **//若是是運算符，調用isOperator
               if ()
               {
                   //從棧中彈出操做數2
                  //從棧中彈出操做數1
                 //根據運算符和兩個操做數調用evalSingleOp計算result;
                   //計算result入棧;
               }
               else//若是是操做數
                   //操做數入棧;
             }**

             return result;
           }

           private boolean isOperator (String token)
           {
             return ( token.equals("+") || token.equals("-") ||
                      token.equals("*") || token.equals("/") );
           }

           private int evalSingleOp (char operation, int op1, int op2)
           {
             int result = 0;

             switch (operation)
                    {
               case ADD:
                 result = op1 + op2;
                 break;
               case SUBTRACT:
                 result = op1 - op2;
                 break;
               case MULTIPLY:
                 result = op1 * op2;
                 break;
               case DIVIDE:
                 result = op1 / op2;
             }

             return result;
           }
  }

填寫的代碼是：
//若是是運算符，調用isOperator
if ()
{
//從棧中彈出操做數2
//從棧中彈出操做數1
//根據運算符和兩個操做數調用evalSingleOp計算result;
//計算result入棧;
}
else//若是是操做數
//操做數入棧;
}

//當輸入是運算符
調用isOperator方法片斷所輸入的是否爲運算符，是運算符則爲true，不是則爲false，當是運算符的時候進行出棧、運算、將結果進棧的操做

根據提示信息和棧的基礎操做，從棧中彈出一個數字爲stack.pop()，並將此值賦給int a,

根據所給的evalSingleOp對前兩個操做數進行加減乘除，並用charAt(0)方法取得字符串的運算符號，進行相應的運算。

碼雲連接