我应该编写一个程序来将中缀转换为后缀。它适用于某些人,但有时不正确。特别是在包含括号的中缀表达式上。谁能给我一个线索,为什么这是错误的?例如,中缀表达式
( ( 5 + 5 * ( 6 - 2 ) + 4 ^ 2 ) * 8 )
返回5562-*42^++8*((2
。
import java.io.*;
import java.util.Scanner;
public class InfixToPostfix
{
//class attributes
private char curValue;
private String postfix;
private LineWriter lw;
private ObjectStack os;
//constructor
public InfixToPostfix(LineWriter l, ObjectStack o)
{
curValue = ' ';
lw=l;
os=o;
}
public String conversion(String buf)
{
String temp =" ";
StringBuffer postfixStrBuf= new StringBuffer(temp);
char popped= new Character(' ');
char topped=' ';
for (int i=0; i<buf.length(); i++)
{
curValue= buf.charAt(i);
if (curValue == '(')
os.push(curValue);
if (curValue == ')')
{
while (popped != '(')
{
popped = ((Character)os.pop());
if (popped != '(')
postfixStrBuf.append(popped);
}
}
if (isOperator(curValue))
{
if( os.isEmpty())
os.push((Character)(curValue));
else
topped=((Character)os.top());
if ( (priority(topped)) >= (priority(curValue)) && (topped != ' ') )
{
popped = ((Character)os.pop());
if (popped != '(')
postfixStrBuf.append(popped);
//if it is a left paranthess, we want to go ahead and push it anyways
os.push((Character)(curValue));
}
if ( (priority(topped)) < (priority(curValue)) && (topped != ' ') )
os.push((Character)(curValue));
}
else if (!isOperator(curValue) && (curValue != ' ') && (curValue != '(' ) && (curValue != ')' ))
postfixStrBuf.append(curValue);
}
//before you grab the next line of the file , pop off whatever is remaining off the stack and append it to
//the infix expression
getRemainingOp(postfixStrBuf);
return postfix;
//postfixStrBuf.delete(0, postfixStrBuf.length());
}
public int priority(char curValue)
{
switch (curValue)
{
case '^': return 3;
case '*':
case '/': return 2;
case '+':
case '-': return 1;
default : return 0;
}
}
public boolean isOperator(char curValue)
{
boolean operator = false;
if ( (curValue == '^' ) || (curValue == '*') || (curValue == '/') || (curValue == '+' ) || (curValue == '-') )
operator = true;
return operator;
}
public String getRemainingOp(StringBuffer postfixStrBuf)
{
char popped=' ';
while ( !(os.isEmpty()) )
{
opped = ((Character)os.pop());
postfixStrBuf.append(popped);
}
postfix=postfixStrBuf.toString();
return postfix;
}
}