使用堆栈将中缀转换为后缀时，结果会有所不同，具体取决于我要传递的数组中的字符串

问题描述

我正在使用堆栈来转换具有以下表达式的数组：所有数字，方括号和运算符都以infix顺序分开。我将此数组传递给“ topPostFix”方法，该方法使用堆栈将数组按后缀顺序转换为String表达式。

`public static String toPostFix(String[] postfixArray){ //converts to post fix with seperated string
        Stack <String> stackPost = new Stack();
        String posst;
        StringBuilder buildtest = new StringBuilder("");
        for(int i=0; i<(postfixArray.length);i++){

            if (isNum(postfixArray[i])){
                buildtest.append(postfixArray[i]);
                buildtest.append(" ");
            }
            else if(isOperator(postfixArray[i])){
                    while(!stackPost.empty() && stackPost.peek()!="(" &&higherPresedance((stackPost.peek()),postfixArray[i])){
                        buildtest.append((stackPost.peek()));
                        buildtest.append(" ");
                        stackPost.pop();
                    }
                    stackPost.push(postfixArray[i]);
                }
            

            else if(postfixArray[i]=="("){
                stackPost.push(postfixArray[i]);
            }

            else if(postfixArray[i]==")"){
                while(!stackPost.empty()&&stackPost.peek()!="("){
                    buildtest.append(stackPost.peek());
                    buildtest.append(" ");
                    stackPost.pop();
                }
                stackPost.pop();
            }
        }

            while(!stackPost.empty()){
                buildtest.append((stackPost.peek()));
                buildtest.append(" ");
                stackPost.pop();
            }

            System.out.println(buildtest);
            posst=buildtest.toString();
            return posst;
        }`

I have individually tested the isNum,isOperator,higherPrecedance methods etc and I kNow they all work individually.

When I pass a test array e.g.(String[] testPost = {"(","-5.4","-","3",")","*","2"}; the result comes out as expected (-5.4 3 - 2 *)

However in my code I want the user to be able to pass a string into the program so I convert the string into the array which when using Arrays.toString(string_converted_to_array). shows up to be '[(,-5.4,-,3,),*,2]'
Where each of the elements in this array is a string.

I have also printed the elements individually using for loops and each element came out on its own without a space. 

However when I pass this "string_converted_to_array" into my toPostFix method it does not come out in the correct postfix notation but instead as -5.4 3 2 * -

I have searched all over the internet and I sincerely promise I have tried all I can to find a solution. Please forgive me if this has already been answered and thank you for you time in advance if you try to find a solution to my problem. If anything needs clarification please let me kNow. 

解决方法

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