程序编译但不打印结果

Question

TL:DR program compiles but results do not print out

Hi, I am working on this assignment for my 1st year programming class. Here is the question:

: In this problem, you need to compute compound interest for various interest rates and various time periods. More precisely, this means that given an amount to invest and an interest rate (a specific amount above the prime interest rate, which for this assignment is 1.00 percent), compute the amount of money an individual would have after n years. The formula to calculate this is given by:

final amount = amount(1.0 + (prime+rate/100.0)^n)

we need to invoke another class in this assignment from a prebuilt so the class they gave us was

import java.util.*;

//DO NOT PUT OTHER METHODS IN THIS CLASS or make any changes to it

public class UserInteraction
{

    public String getStringValueFromUser(String message)

    {

        String value = "";

        Scanner input = new Scanner(System.in);

        System.out.print(message + " : ");

        value = input.nextLine();

        return value;

    }

    //DO NOT PUT OTHER METHODS IN THIS CLASS or make any changes to it

    public double getDoubleValueFromUser(String message)

    {

       double value = 0;

       Scanner input = new Scanner(System.in);

       System.out.print(message + " : ");

       value = input.nextDouble();

       return value;

    }

   //DO NOT PUT OTHER METHODS IN THIS CLASS or make any changes to it

   public int getIntValueFromUser(String message)

   {

       int value = 0;

       Scanner input = new Scanner(System.in);

       System.out.print(message + " : ");

       value = input.nextInt();

       return value;

   }


    //DO NOT PUT OTHER METHODS IN THIS CLASS or make any changes to it

}

and my code is here

 import java.util.*;

 public class InterestRate

 {

    UserInteraction input =  new UserInteraction();

    public static void main (String[] args)

    {

       InterestRate program = new InterestRate();

       program.execute();

    }
    void execute()
    {
         double initial_money = input.getDoubleValueFromUser("Your initial amount");
         double prime_rate = input.getDoubleValueFromUser("Enter the Prime Rate");
         double InterestRate = input.getDoubleValueFromUser("Enter the Interest Rate as a value above prime");
         double time = input.getDoubleValueFromUser("Enter the length of the investment in years to a decimal");
         double InterestRate2 = input.getDoubleValueFromUser("Enter the second Interest Rate as a value above prime");

         Calculations (initial_money, prime_rate, InterestRate, time);
         Calculations2 (initial_money, prime_rate, InterestRate2, time);


    }

    void finaltotal(double totalrate4, double totalrate4a, double initial_money, double prime_rate, double InterestRate, double time, double InterestRate2)

    {
        double final_amount = (initial_money * totalrate4);
        double final_amounta = (initial_money * totalrate4a);

        printWinnings(final_amount, initial_money, InterestRate, prime_rate, final_amounta, time);
    }

    double Calculations(double initial_money, double prime_rate, double InterestRate, double time)
    {
       double totalrate = prime_rate + InterestRate;
       double totalrate2 = totalrate / 100.0;
       double totalrate3 = totalrate2 + 1.0;
       double totalrate4 = Math.pow(time, totalrate3);


       return totalrate4;


    }
    double Calculations2(double initial_money, double prime_rate, double InterestRate2, double time)
    {
       double totalrate1a = prime_rate + InterestRate2;
       double totalrate2a = totalrate1a / 100.0;
       double totalrate3a = totalrate2a + 1.0;
       double totalrate4a = Math.pow(time, totalrate3a);
       //double final_amounta = initial_money * totalrate4;

       return totalrate4a; 

    }

    void printWinnings(double final_amount, double initial_money, double prime_rate, double InterestRate, double time, double final_amounta)

    {
        System.out.println(" The amount of money you can expect to get over the " + time + " years you invest will be " + final_amount + " with your initial investment of  " + initial_money + " at an rate of " + InterestRate);

    }
}

So I typed it all up, and the program compiles, but when I run it, nothing prints out.

Answer 1

Technically you didn't ask a question you made a statement. I assume you meant to ask why your program does not produce any output of results after the initial prompts for input.

If you follow the execution of your code it goes like this:

The main method is executed first:

public static void main(String[] args)
{
    InterestRate program = new InterestRate();
    program.execute();
}

As you can see your execute method is called from main , so now the execution goes here:

void execute() {
    double initial_money = input
            .getDoubleValueFromUser("Your initial amount");
    double prime_rate = input
            .getDoubleValueFromUser("Enter the Prime Rate");
    double InterestRate = input
            .getDoubleValueFromUser("Enter the Interest Rate as a value above prime");
    double time = input
            .getDoubleValueFromUser("Enter the length of the investment in years to a decimal");
    double InterestRate2 = input
            .getDoubleValueFromUser("Enter the second Interest Rate as a value above prime");

    Calculations(initial_money, prime_rate, InterestRate, time);
    Calculations2(initial_money, prime_rate, InterestRate2, time);

}

Before I move on I just want to mention that naming methods so that they begin with a capital letter violates accepted Java standard naming practice . Methods are always named using camel case and starting with lowercase. Similarly, naming variables in this manner also violates the naming conventions of Java. For example, InterestRate should be interestRate because otherwise it reads like a class name. Generally only constants use underscores between words so things like initial_money would be more consistent with naming convention if written as initialMoney .

Getting back to your code - from where we left off your logic flows into Calculations and Calculations2 :

double Calculations(double initial_money, double prime_rate,
        double InterestRate, double time) {
    double totalrate = prime_rate + InterestRate;
    double totalrate2 = totalrate / 100.0;
    double totalrate3 = totalrate2 + 1.0;
    double totalrate4 = Math.pow(time, totalrate3);

    return totalrate4;

}

double Calculations2(double initial_money, double prime_rate,
        double InterestRate2, double time) {
    double totalrate1a = prime_rate + InterestRate2;
    double totalrate2a = totalrate1a / 100.0;
    double totalrate3a = totalrate2a + 1.0;
    double totalrate4a = Math.pow(time, totalrate3a);
    // double final_amounta = initial_money * totalrate4;

    return totalrate4a;

}

Now you will notice none of these methods have any calls to System.out.print or System.out.println . This is why you don't see any output.