Java 将中缀表达式转换成后缀表达式

﹏ヽ暗。殇╰゛Y 2023-07-23 14:00 49阅读 0赞

###### 使用堆栈进行表达式的堆栈将中缀（Infix）表达式转换成后缀（postfix）表达式 ######

**完整代码**

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);
         }
       }
    }

结果输出

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