20155226 mini DC 课堂测试补交

由于电脑突然出了点问题，我没有完成mini DC这个测试，现将测试内容及结果补交

题目如下

提交测试截图和码云练习项目链接，实现Linux下dc的功能，计算后缀表达式的值

• 代码如下
  • MyDC.class

import com.sun.xml.internal.fastinfoset.util.CharArray;
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();
            //如果是运算符，调用isOperator
            if (isOperator(token)==true) {
                op2=stack.pop();
                op1=stack.pop();
                //从栈中弹出操作数2
                //从栈中弹出操作数1
                result=evalSingleOp(token.charAt(0),op1,op2);
                //根据运算符和两个操作数调用evalSingleOp计算result;
                stack.push(result);
                //计算result入栈;
            }
            else//如果是操作数
            {
                stack.push(Integer.parseInt(token));
            }
            //操作数入栈;
        }

        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;
    }
}

* **MyDCTester.class**

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 ("That expression equals " + result);
                         System.out.print ("Evaluate another expression [Y/N]? ");
                       again = in.nextLine();
                      System.out.println();
                      }
                 while (again.equalsIgnoreCase("y"));
              }![](http://images2015.cnblogs.com/blog/1071653/201705/1071653-20170503220452023-968944949.jpg)

            catch (Exception IOException)
         {
                 System.out.println("Input exception reported");
            }
        }
 }

• 测试截图

• 代码链接