java - 我收到变量 isOperator 的编译错误是什么？

Question

每当我为我的项目编译此代码时，它总是会出现错误。我正在尝试为我的编程课编写一个实际的计算器。当我编译它时，bluej 说“它找不到符号 - 变量 isOperator”。

import java.util.*;
public class InfixtoPostFix
{
    // instance variables - replace the example below with your own
    //insert nested class SyntaxErroeException.
    public static class SyntaxErrorException extends Exception{
        SyntaxErrorException (String message){
            super(message);
        }
    }
    //data fields
    /**The operator Stack */
    private Stack<Character> operatorStack;
    /** THe operator */
    private static final String OPERATORS = "+-*/";
    /** The precedence of the operators mathces the order in Operators */
    private static final int[] PRECENDENCE = {0,1,1,2,2,2};
    /** Postfix string */
    private StringBuilder postfix;

    public String convert(String infix) throws SyntaxErrorException{
        operatorStack = new Stack<Character>();
        postfix = new StringBuilder();

        String[] tokens = infix.split("\\s+");
        //process each token in the infix string
        try{
            for(String nextToken : tokens){
                char firstChar = nextToken.charAt(0);
                //is it an operand
                if(Character.isJavaIdentifierStart(firstChar) || Character.isDigit(firstChar)){
                    postfix.append(nextToken);
                    postfix.append(' ');
                }else if(isOperator(firstChar)){
                    //is it an operator
                    processOpperator(firstChar);
                }else{
                    throw new SyntaxErrorException("Unexpected Character Encountered: " + firstChar);
                }
            }

            //pop any remaing opperators
            //appen them to post fix
            while(!operatorStack.empty()){
                char op = operatorStack.pop();
                postfix.append(op);
                postfix.append(' ');
            }

            //assert =: stack is empty return result
            return postfix.toString();
        }catch(EmptyStackException e){
            throw new SyntaxErrorException("Syntax error: The stack is empty");
        }
    }

    private void processOpperator(char op){
        if(operatorStack.empty()){
            operatorStack.push(op);
        }else{
            //peek the operator stack and ler topOp be the top operator
            char topOp = operatorStack.peek();
            if(precedence(op) > precedence(topOp)){
                operatorStack.push(op);
            }else{
                //pop all stacked operators with equal or higher prededence than op
                while(!operatorStack.empty() && precedence(op) <= precedence(op)){
                    operatorStack.pop();
                    postfix.append(topOp);
                    postfix.append(' ');
                    if(!operatorStack.empty()){
                        topOp = operatorStack.peek();
                    }
                }
                //assert: operator stack is empty or current operator precedence > top of stack operator preceence
                operatorStack.push(op);
            }
        }
    }

    private boolean isOperator(char ch){
        return isOperator.indexOf(ch) != 1;
    }

    private int precedence(char op){
        return PRECEDENCE[OPERATORS>indexOf(op)];
    }

}

Answer 1

在方法 isOperator 中，您编写:return isOperator.indexOf(ch) != 1;，您使用名为 isOperator 的变量，但我认为您应该使用静态成员变量 OPERATORS；我想你应该将 indexOf 的返回值与 -1 进行比较，而不是 1，如果你想检查 ch 是否存在于 OPERATORS 中，所以改变

private boolean isOperator(char ch){
    return isOperator.indexOf(ch) != 1;
}

至

private boolean isOperator(char ch){
    return OPERATORS.indexOf(ch) != -1;
}