我想解決錯誤的解析成一個數學表達式解決java程序中的雙重

Question

我是一個java初學者。而且我沒有Java中複雜編碼的能力。 我想製作一個程序來解決以字符串形式給出的數學表達式，其中只能包含數字和四個基本的算術運算符。 我已經寫了下面的代碼，我知道的基本知識。但是當我運行代碼時，它顯示錯誤。它說我不能解析對象到雙等...

我試圖根據BODMAS規則給予四個基本操作符的優先權。 但我不知道如何用括號括住表達式的括號優先。

下面的代碼對於那些只需要幾行代碼的專家來說似乎很有趣，但我真的是一個初學者。

這裏是我做的代碼： （註釋不寫，因爲這代碼很簡單，任何人都可以理解）

import java.util.*; 
import java.util.concurrent.TimeUnit; 
class Calculator 
{ 
public static void main(String[] args) 
throws Exception 
{ 
    int aaa =0; 
    while(aaa==0){ 
     Scanner sc = new Scanner(System.in); 
     System.out.println("\nEnter expression to solve : "); 
     String expression = sc.nextLine(); 
     if(!expression.isEmpty()){ 
      int charlength = expression.length(); 
      String charat0 = ""+expression.charAt(0); 
      String charatlast = ""+expression.charAt(charlength-1); 
      ArrayList forops = new ArrayList(); 
      ArrayList forchars = new ArrayList(); 
      if(expression.contains(" ")){ 
       pWD("\nSpaces are not allowed",TimeUnit.MILLISECONDS,30); 
      }else if(!expression.matches("[-+/*0-9]+")){ 
       pWD("\nEnter only numbers and operators",TimeUnit.MILLISECONDS,30); 
      }else if(!charat0.matches("[0-9]+")||!charatlast.matches("[0-9]+")){ 
       pWD("first and last characters must be\nnumbers",TimeUnit.MILLISECONDS,30); 
      }else if(expression.contains("//")||expression.contains("**")||expression.contains("--")||expression.contains("++")|| 
        expression.contains("/+")||expression.contains("*/")||expression.contains("-*")||expression.contains("+-")|| 
        expression.contains("/-")||expression.contains("*+")||expression.contains("-/")||expression.contains("+*")|| 
        expression.contains("/*")||expression.contains("*-")||expression.contains("-+")||expression.contains("+/")){ 
       pWD("There must be SINGLE operator between\ntwo adjacent numbers",TimeUnit.MILLISECONDS,30); 
      }else{ 
       String[] chararr = expression.split("(?<=[-+*/])|(?=[-+*/])"); 
       int chararrl =chararr.length; 
       for(int nn=0;nn<chararrl;nn++){ 
        forchars.add(chararr[nn]); 
       }for(int mn=0;mn<chararrl;mn+=2){ 
        String willparse = ""+forchars.get(mn); 
        double parseint= Double.parseDouble(willparse); 
        forchars.set(mn,parseint); 
       }while(forchars.contains("/")){ 
        int divindex = forchars.indexOf("/"); 
        double prediv = forchars.get(divindex-1); 
        double nexdiv = forchars.get(divindex+1); 
        forchars.set(divindex,(prediv/nexdiv)); 
        forchars.remove(forchars.indexOf(prediv)); 
        forchars.remove(forchars.indexOf(nexdiv)); 
       }while(forchars.contains("*")){ 
        int mulindex = forchars.indexOf("*"); 
        double premul = forchars.get(mulindex-1); 
        double nexmul = forchars.get(mulindex+1); 
        forchars.set(mulindex,(premul*nexmul)); 
        forchars.remove(forchars.indexOf(premul)); 
        forchars.remove(forchars.indexOf(nexmul)); 
       }while(forchars.contains("-")){ 
        int subindex = forchars.indexOf("-"); 
        double presub = forchars.get(subindex-1); 
        double nexsub = forchars.get(subindex+1); 
        forchars.set(subindex,(presub-nexsub)); 
        forchars.remove(forchars.indexOf(presub)); 
        forchars.remove(forchars.indexOf(nexsub)); 
       }while(forchars.contains("+")){ 
        int addindex = forchars.indexOf("+"); 
        double preadd = forchars.get(addindex-1); 
        double nexadd = forchars.get(addindex+1); 
        forchars.set(addindex,(preadd+nexadd)); 
        forchars.remove(forchars.indexOf(preadd)); 
        forchars.remove(forchars.indexOf(nexadd));} 
       double answer1 = forchars.get(0); 
       String answer = Double.toString(answer1); 
       pWD("\nFinal answer is : "+answer,TimeUnit.MILLISECONDS,80); 
      }}else{ 
      pWD("Please enter something",TimeUnit.MILLISECONDS,30); 
     }} 
}public static void pWD(String data, TimeUnit unit, long delay) 
throws InterruptedException { 
    for (char ch:data.toCharArray()) { 
     System.out.print(ch); 
     unit.sleep(delay); 
     } 
    } 
} 

請幫我如何解決解析成雙重的錯誤。 如果用戶將表達式括在括號中，請詳細解釋如何解決表達式。

謝謝。

Answer 1

由於您聲明瞭double變量，因此無法爲其分配int值。所以，我想你應該有最好的選擇是：

投你int到double

double prediv = (double) forchars.get(divindex - 1); 

這僅僅是你應該考慮的類型不匹配。