BigDecimal Class Java

Question

我正在嘗試使用BigDecimal類爲學校編寫一個程序。該計劃是利率計算器和最終的輸出應該像somethig：

Loan Amount: whatever loan amount is in dollars 
    Interest Rate: as a percent 
    Interest: amount of interest paid in dollars 
    continue? Y/N: 

這本書不是關於如何編寫BigDecimal類清楚，我使用Eclipse，因此任何時候，我做出改變我收到一個令人困惑的錯誤。 有人可以看看這個，並讓我在正確的方向嗎？我正在使用Murach的Java SE6，這本書不是很有幫助。

謝謝！

import java.util.Scanner;   //import scanner 
    import java.text.NumberFormat;  //import number format 
    import java.math.*;     //import math classes 


    public class InterestCalculator  //create public class 
    { 

     public static void main(String[] args) 
      { 
      Scanner calc = new Scanner(System.in); //create scanner 
      double LoanAmount, InterestRate, Interest; //declareLoanAmount,InterestRate, and Interest as double 

      //welcome user to the Interest Rate Calculator 
      System.out.println("Welcome to The Interest Rate Calculator"); 
      System.out.println(); 
      //perform choice calculations until choice isn't equal to "y" or "Y" 
      String choice = "y";  
      while (choice.equalsIgnoreCase("y")) 
       { 

       //Get Loan Amount from user 
       System.out.println("Enter Loan Amount: "); 
       LoanAmount = calc.nextDouble(); 

       //Get Interest rate from user 
       System.out.println("Enter Interest Rate: "); 
       InterestRate = calc.nextDouble(); 

       BigDecimal decimalInterest = new BigDecimal(Double.toString(Interest)); 
       decimalInterest = decimalInterest.setScale(2, RoundingMode.HALF_UP); 
       BigDecimal decimalInterestRate = new BigDecimal(Double.toString(InterestRate)); 
       decimalInterestRate = decimalInterestRate.setScale(2, RoundingMode.HALF_UP); 

       //calculate interest 



       System.out.println("message"); 


       //prompt user to continue? 
       System.out.println("Continue? Y/N: "); 
       choice = calc.next(); 
       System.out.println(); 



       } 


     } 

    } 

Answer 1

你的問題涉及到這一點

BigDecimal decimalInterest = new BigDecimal(Double.toString(Interest)); 

變量的興趣並不在這一點上initalized。

像這樣的東西應該做的工作（但我沒有提高你的編碼風格）：

 BigDecimal decimalInterestRate = new BigDecimal(Double.toString(InterestRate)); 
     decimalInterestRate = decimalInterestRate.setScale(2, RoundingMode.HALF_UP); 
     BigDecimal decimalLoanAmount = new BigDecimal(Double.toString(LoanAmount)); 
     decimalLoanAmount = decimalLoanAmount.setScale(2, RoundingMode.HALF_UP); 

     // calculate interest 
     BigDecimal Interest = decimalInterestRate.multiply(decimalLoanAmount); 

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

附：您需要在主方法的開始處刪除Interest聲明。