Java超出範圍

我的程序幾乎完成，除了一個問題。我在for循環中遇到了一個超出範圍的問題。該計劃的目標是綜合每月用戶輸入金額&期限的利息。Java超出範圍

在5000 $本金5％的輸出的例子爲3年利息爲：

Month: Interest: Principal: 
1  $20.83  $5020.83 
2  $20.92  $5041.75 
etc  etc   etc 

Starting Balance  = $ 5000.00 // having problem outputting these w/ for-loop 
Final Account Balance = $ 5807.36 // System.out.print keeps repeating multiple times 
Total Interest Paid  = $ 807.36 // but i can't use variables outside of loop

我的問題是，在我的for循環中，我一直在輸出期初餘額，最後的平衡和總利息每次程序都經過循環。但如果我嘗試在循環外部使用變量，它將超出範圍，如果我嘗試在循環外部聲明變量，則不能在循環內部使用它們，因爲它已在構造函數中聲明。

任何人都可以給我一些提示或建議嗎？

我的代碼：

public class Calculator 
{ 

    public Calculator() 
    { 
     Scanner input = new Scanner(System.in); 
     boolean error = false; 

     while (!error){ 
     System.out.print("Please input the following: principal, interest rate, term >> "); 
     double principal = input.nextDouble(); 
     double interest_rate = input.nextDouble(); 
     int term = input.nextInt(); 
     String Month = input.next(); 


     char dollar_sym = 36; 

     if (interest_rate <= 0 || term <= 0 || principal <= 0) // input validation 
      { 
      System.out.println("The term, interest rate and principal must be greater 
      than zero"); 
      continue; 
      } 
     if (!Month.equals("month")) // input validation 
      { 
      System.out.println("Please input month after term"); 
      continue; 
      } 

     System.out.println("Month: " + " Interest: " + "Principal: "); 

     if (Month.equals("month")) 
     { 
      for (int month = 1; month <= term; month++) 
      { 
       double interest = (principal * interest_rate/100)/12; 
       principal = principal + interest; 

       System.out.printf("%4d  %c%5.2f %c%5.2f\n", month, 
       dollar_sym, interest, dollar_sym, principal); 

       double start_principal = principal - interest; // problem 
       double final_principal = principal; // problem 
       double total_interest = interest * interest_rate; // problem 

       System.out.println(" Starting balance = " + start_principal); // problem 
       System.out.println("Final account balance = " + final_principal); // problem 
       System.out.println("Total Interest Paid = " + total_interest); // problem 
      } 
     } 
     } 
    } 
    }

來源

2014-11-04 Maxwell1222

看看這個[教程]（http://www.cs.umd.edu/~clin/MoreJava/ControlFlow/block.html）。 – MarsAtomic 2014-11-04 02:29:48

謝謝，我會看看。 – Maxwell1222 2014-11-04 02:35:57

聲明他們在循環開始之前，所以他們會存在內環路和之後：

double start_principal = 0; 
double final_principal = 0; 
double total_interest = 0; 

Scanner input = new Scanner(System.in); 
boolean error = false; 

while (!error) { 
    // ... 
} 

// ...

來源

2014-11-04 02:29:09 karlphillip

在我的回答，我假設當你說goes out of scope時，你的意思是你得到了編譯時錯誤。（注意，如果您提供了錯誤消息和導致錯誤消息的行，它將使答案更容易解決）。

變量的範圍指的是變量可訪問的地方。例如，如果聲明是if語句中的一個變量，則範圍是即if語句。一些示例代碼：

public void updateStatus(){ 
    Boolean shouldCheckStatus = true;//this variable is declared inside of the updateStatus method, so that is the scope of the variable 
    if(shouldCheckStatus == true){ 
     Int hitCounter = 0;//this variable is declared inside of the if statement, so it is only accessible inside of the if statement 
     //do some work 
     if(hitCounter > 100){ 
      self.registerHits(hitCounter);//hitCounter is still accessible here, because it is still inside of the if statement 
     } 
     else{ 
      shouldCheckStatus = false; 
     } 
    }//close the if statement and so close the scope... 
    //the hitCounter variable is no longer in scope, because we are no longer in the if statement 
    //but shouldCheckStatus is still in scope, because we are still in the method 
    if(shouldCheckStatus == true){ 
     self.callAnotherMethod(); 
    } 
}

所以你的問題，你需要聲明以上要使用它，你想用它的範圍內您的變量。然後不要再聲明。所以在循環之前聲明。

來源

2014-11-04 02:34:10

Java超出範圍

回答

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