Java 实例 - 利用堆栈将中缀表达式转换成后缀表达式

InToPost.java 文件

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);
     }
   }
}

124*5/+7-36/+
Postfix is 124*5/+7-36/+