中缀表达式变换为后缀表达式

中缀表达式转换为后缀表达式

操作数?????????????????? ? ? ? ? ? ? ? ? ? ? ? ?? ?????????? 写至输出

左括号 ????????????????????????????????????????????????????? 推入栈

右括号?????????????????????????????????????????????????????? 栈非空时，重复以下步骤

?????????????????????????????????????????????????????????????? ? ? 弹出一项，

?????????????????????????????????????????????????????????????? ? ? 若不为左括号，则opTop写至输出

?????????????????????????????????????????????????????????????? ? ? 若为左括号，则退出循环

当前读取的操作符opThis ???????????????????????????? 若栈为空，则存入栈

????????????????????????????????????????????????????????????? ? 若非空，重复以下步骤

?????????????????????????????????????????????????????????????????? 弹出一项opTop

?????????????????????????????????????????????????????????????????? 若为左括号，则左括号和当前操作符都存入栈，退出循环

?????????????????????????????????????????????????????????????????? 若为操作符，且

???????????????????????????????????????????????????????????????????????? 若opTop>=opThis，则opTop存入栈，输出opThis

???????????????????????????????????????????????????????????????????????? 若opTop<opThis 则输出opTop

没有更多项??????????????????????????????????????????? 当栈非空时，弹出项目，将其输出

?

?

public String doTrans() // do translation to postfix{for (int j = 0; j < input.length(); j++) // for each char{char ch = input.charAt(j); // get ittheStack.displayStack("For " + ch + " "); // *diagnostic*switch (ch) {case '+': // it's + or -case '-':gotOper(ch, 1); // go pop operatorsbreak; // (precedence 1)case '*': // it's * or /case '/':gotOper(ch, 2); // go pop operatorsbreak; // (precedence 2)case '(': // it's a left parentheStack.push(ch); // push itbreak;case ')': // it's a right parengotParen(ch); // go pop operatorsbreak;default: // must be an operandoutput = output + ch; // write it to outputbreak;} // end switch} // end forwhile (!theStack.isEmpty()) // pop remaining opers{theStack.displayStack("While "); // *diagnostic*output = output + theStack.pop(); // write to output}theStack.displayStack("End   "); // *diagnostic*return output; // return postfix         }

?

public void gotOper(char opThis, int prec1) { // got operator from inputwhile (!theStack.isEmpty()) {char opTop = theStack.pop();if (opTop == '(') // if it's a '('{theStack.push(opTop); // restore '('break;} else // it's an operator{int prec2; // precedence of new opif (opTop == '+' || opTop == '-') // find new op precprec2 = 1;elseprec2 = 2;if (prec2 < prec1) // if prec of new op less{ // than prec of oldtheStack.push(opTop); // save newly-popped opbreak;} else// prec of new not lessoutput = output + opTop; // than prec of old} // end else (it's an operator)} // end whiletheStack.push(opThis); // push new operator        }

public void gotParen(char ch) { // got right paren from inputwhile (!theStack.isEmpty()) {char chx = theStack.pop();if (chx == '(') // if popped '('break; // we're doneelse// if popped operatoroutput = output + chx; // output it} // end while} // end popOps()124+5*+// --------------------------} // end class InToPost