Java示例Infix到Postfix

import java.io.IOException;



public class InToPost {

   private Stack theStack;

   private String input;

   private String output = "";

   public InToPost(String in) {

      input = in;

      int stackSize = input.length();

      theStack = new Stack(stackSize);

   }

   public String doTrans() {

      for (int j = 0; j < input.length(); j++) {

         char ch = input.charAt(j);

         switch (ch) {

            case '+':

            case '-':

               gotOper(ch, 1);

               break;

            case '*':

            case '/':

               gotOper(ch, 2);

               break;

            case '(':

               theStack.push(ch);

               break;

            case ')':

               gotParen(ch);

               break;

            default:

               output = output + ch;

               break;

         }

      }

      while (!theStack.isEmpty()) {

         output = output + theStack.pop();

      }

      System.out.println(output);

      return output;

   }

   public void gotOper(char opThis, int prec1) {

      while (!theStack.isEmpty()) {

         char opTop = theStack.pop();

         if (opTop == '(') {

            theStack.push(opTop);

            break;

         } else {

            int prec2;

            if (opTop == '+' || opTop == '-')

            prec2 = 1;

            else

            prec2 = 2;

            if (prec2 < prec1) {

               theStack.push(opTop);

               break;

            }

            else output = output + opTop;

         }

      }

      theStack.push(opThis);

   }

   public void gotParen(char ch) {

      while (!theStack.isEmpty()) {

         char chx = theStack.pop();

         if (chx == '(')

         break;

         else output = output + chx;

      }

   }

   public static void main(String[] args) throws IOException {

      String input = "1+2*4/5-7+3/6";

      String output;

      InToPost theTrans = new InToPost(input);

      output = theTrans.doTrans();

      System.out.println("Postfix is " + output + '\n');

   }

   class Stack {

      private int maxSize;

      private char[] stackArray;

      private int top;



      public Stack(int max) {

         maxSize = max;

         stackArray = new char[maxSize];

         top = -1;

      }

      public void push(char j) {

         stackArray[++top] = j;

      }

      public char pop() {

         return stackArray[top--];

      }

      public char peek() {

         return stackArray[top];

      }

      public boolean isEmpty() {

         return (top == -1);

      }

   }

}