使用两个堆栈的java中缀到后缀

Question

我的评估方法需要帮助。我得到的结果是完全错误的。我的代码是这样做的：输入：（5+3）*3输出：操作数堆栈：[（，5，+3+，），*4*]运算符堆栈：[]输出应该是：操作数堆栈：[5 3+4*]运算符堆栈：[]*注意：数字之间应该有空格

以下是我的评估方法：

/** * Evaluates the specified postfix expression. If an operand is encountered, * it is pushed onto the operand stack. If an operator is encountered, two * operands are popped, the expression is evaluated, and the result is * pushed onto the operand stack. * * @param expr string representation of a postfix expression * @return value of the given expression */ public String evaluate(String expr) { // A variable to hold the resulting postfix expression. String result; // A string variable to hold the individual elements of user's input string. String token; // A parser to read the individual tokens of user input, tokens must be separated by whitespace. Scanner parser = new Scanner(expr); while (parser.hasNext()) { // Evaluating the expression one token at a time. token = parser.next(); // 1) An operand is either the first or second operand for an operator. // If the operator stack is empty or if a left parenthesis is on top of the stack, // the operand is the first operand for an operator. Push the operand onto the operand stack. if (operatorStack.isEmpty() || operatorStack.peek().equals("(")) { // Operand 1 operand1 = token; // Pushing operand1 onto the operand stack operandStack.push(operand1); } // 1) Otherwise, the operand is the second operand for an operator. The first operand should be on top of // the operand stack, and the operator should be on top of the operator stack. Pop the // first operand and the operator from the stacks, and form the postfix expression // representing applying the operator to its two operands. This expression is an operand // to which another operator may be applied, so push it onto the operand stack. else { // Operand 2 String operand2 = token; // Popping current operator and operand1 operand1 = operandStack.pop(); currentOperator = operatorStack.pop(); // Forming the resulting expression resultingExpression = (operand1 + " " + operand2 + " " + currentOperator + " "); // Pushing the resulting expression onto the operandStack operandStack.push(resultingExpression); } // 2) A right parenthesis marks the end of an infix operand expression. The matching left // parenthesis should be on top of the operator stack, and the postfix operand expression // corresponding to the infix operand expression should be on top of the operand stack. // Pop the left parenthesis off the operator stack. If the stack is now empty or if the token // on top of the stack is another left parenthesis, the operand on top of the operand stack // is the first operand for an operator, assuming the end of the whole infix expression has // not been reached. In this case, do nothing further.Otherwise, the postfix expression // on top of the operand stack is the second operand for an operator. // The first operand should be immediately below it, and the operator should be on // top of the operator stack.Pop both operands and the operator from the stacks, and form // the postfix expression representing applying the operator to its operands. As in 1 // above, push this expression onto the operand stack. if (isRightParen(token)) { // Popping left parenthesis operatorStack.pop(); if (operatorStack.isEmpty() || operatorStack.peek().equals("(")) { // First operand for an operator operand1 = operandStack.peek(); } else { // Second operand for an operator operand2 = operandStack.peek(); // Pop both operands operandStack.pop(); operandStack.pop(); // Pop operator currentOperator = operatorStack.pop(); // Forming the resulting expression resultingExpression = (operand1 + " " + operand2 + " " + currentOperator + " "); // Pushing the resulting expression onto the operandStack operandStack.push(resultingExpression); } } // 3) To process an operator or a left parenthesis, simply push it onto the operator stack. // If token is an operator push it on the operator stack. if (isOperator(token)) { operatorStack.push(token); } // If token is a left parenthesis push it on to the operator stack. else if (isLeftParen(token)) { operatorStack.push(token); } } // Returning the completed postfix result result = ("Operand Stack: " + operandStack.toString() + " " + "Operator Stack: " + operatorStack.toString()); return result; }