为什么我必须输入两次数据？

Question

I'm writing this program that will let you enter in an amount for each quarters, dimes, nickels and pennies and return their amount in $. After that, I want to be able to add up the dollar amounts they produce without having to enter in all of the coin amounts a second time. Any ideas? Thanks in advance.

import java.util.*;

public class HalfDollar {
  public static final Scanner CONSOLE = new Scanner(System.in);

  public static void main(String[] args) {
    quarterDollarAmount( );
    dimeDollarAmount( );
    nickelDollarAmount( );
    pennyDollarAmount( );
    totalDollarAmount( );
  }

  public static double quarterDollarAmount( ) {
    System.out.print("Enter the number of quarters: ");
    int quarterDollar = CONSOLE.nextInt( );
    double amount = quarterDollar * 0.25;
    System.out.println(quarterDollar + " Quarter are $" + amount);
    return amount;
  }

  public static double dimeDollarAmount( ) {
    System.out.print("Enter the number of dimes: ");
    int dimeDollar = CONSOLE.nextInt( );
    double amount = dimeDollar * 0.10;
    System.out.println(dimeDollar + " Dimes are $" + amount);
    return amount;
  }

  public static double nickelDollarAmount( ) {
    System.out.print("Enter the number of nickels: ");
    int nickelDollar = CONSOLE.nextInt( );
    double amount = nickelDollar * 0.05;
    System.out.println(nickelDollar + " Nickels are $" + amount);
    return amount;
  }

  public static double pennyDollarAmount( ) {
    System.out.print("Enter the number of pennies: ");
    int pennyDollar = CONSOLE.nextInt( );
    double amount = pennyDollar * 0.01;
    System.out.println(pennyDollar + " Pennies are $" + amount);
    return amount;
  }

  public static double totalDollarAmount( ) {
    double quarter = quarterDollarAmount();
    double dime = dimeDollarAmount();
    double nickel = nickelDollarAmount();
    double penny = pennyDollarAmount();
    double total = quarter + dime + nickel + penny;
    System.out.println("Total amount is $" + total);
    return total;
  }
}

Answer 1

You're not doing anything with your variables. Just calling them and then they're moving out of scope.

You could either store the returned value in a global variable to use later.

private double quarter, dime, total;

public static void main(String[] args) {
     quarter = quarterDollarAmount();
     dime = dimeDollarAmount();
     total = (quarter + dime);
     s.o.p(total);

}

If you don't care about the value after printing it out you can either total them up with local variables or literally just total up your methods as follows.

public static void main(String[] args) {
     s.o.p(quarterDollarAmount( ) + dimeDollarAmount( ) + ....);
}

To get your value to 2 decimal places use something like the following:

DecimalFormat format = new DecimalFormat("#.00");
Double total_formatted = Double.parseDouble(format.format(total));
s.o.p(total_formatted);

That enforces the value to have 2 decimal places with an optional amount of digits left of the decimal place.

Final thing, you probably don't want to make everything static. It basically defeats the point of object orientation as static variable will persist throughout all objects of a class.

Answer 2

Hmmm, this smells to me like a homework problem. If you are truly the one who wrote this code, any number of solutions should be pretty obvious. But whatever, I won't judge your journey. Since you are returning the amount from each method, just keep a running total of all the amounts as you go along, then change your totalDollarAmount method to take the total as input instead of asking for it again:

double total = 0.0;
total += quarterDollarAmount( );
total += dimeDollarAmount( );
total += nickelDollarAmount( );
total += pennyDollarAmount( );
totalDollarAmount( total );