如何计算一大堆不同的扫描仪输入？

Question

I'm not quiet sure how to go about doing the calculations for this. I have everything down right up until i'm trying to actually get the investment amount. I know what i have right now is wrong, but google isn't being super helpful for me, and my book just does not have what i need in order to complete this darn thing.

Here what i have right now

import java.util.Scanner;

class InvestmentCalculator {

    public static void main(String[] args) {

        // create a scanner object
        Scanner input = new Scanner(System.in);

        // Prompt user to enter investment amount
        Scanner amount = new Scanner(System.in);
        System.out.println("Enter Investment Amount");
        while (!amount.hasNextDouble()) {
            System.out.println("Only Integers");
            amount.next();
        }

        //Promt user to enter interest rate
        Scanner interest = new Scanner(System.in);
        System.out.println("Enter Interest Percentage in decimals");
        while (!interest.hasNextDouble()) {
            System.out.println("Just like before, just numbers");
            interest.next();
        }

        //Prompt user to enter number of years
        Scanner years = new Scanner(System.in);
        System.out.println("Enter Number of Years");
        while (!years.hasNextDouble()) {
            System.out.println("Now you are just being silly. Only Numbers allowed");
            years.next();

        }

        //Compute Investment Amount
        double future = amount * Math.pow((1 + interest), (years * 12));

        //Display Results
        System.out.println("Your future investment amount is " + future);

    }
}

Any assistance would be very very helpful!

Answer 1

First of all amount , interest and years are Scanners , they are not numbers. The Scanner could contain any number of different types of content so it's impossible for something like Math.pow to know what it should do with them

You need to assign the values you read from the user to some variables.

I'd start by using a single Scanner , say called kb ...

Scanner kb = new Scanner(System.in);

Then use this whenever you want to get a value from the user...

You input loops seem wrong to me, I'm not particularly experienced with the Scanner , so there is probably a better way to achieve this, but...

int invest = -1; // amount
double rate = -1; // percentage
int period = -1; // period
do {
    System.out.println("Only Integers");
    String text = kb.nextLine();
    try {
        invest = Integer.parseInt(text);
    } catch (NumberFormatException exp) {
        System.out.println("!! " + text + " is not an integer");
    }
} while (invest == -1);
System.out.println(invest);

Once you have all the information you need, make your calculations with these primitive types...

double future = invest * Math.pow((1 + rate), (period * 12));

Answer 2

You don't have to use 4 different scanners for this because you are reading from the same stream.... Your code should be something like this -

import java.util.Scanner;

class InvestmentCalculator {

public static void main(String[] args) {
     double amount=0;
     int interest=0;
     double years=0;
    // create a scanner object
    Scanner input = new Scanner(System.in);

    // Prompt user to enter investment amount
    Scanner amount = new Scanner(System.in);
    System.out.println("Enter Investment Amount");
    while (!input.hasNextDouble()) {      // you say you only want integers and are           
                                          // reading double values??
        System.out.println("Only Integers");
        amount = input.nextDouble();   
    }

    //Promt user to enter interest rate
    System.out.println("Enter Interest Percentage in decimals");
    while (!input.hasNextInt()) {
        System.out.println("Just like before, just numbers");
      interest= input.nextInt();
    }

    //Prompt user to enter number of years
    System.out.println("Enter Number of Years");
    while (!input.hasNextDouble()) {
        System.out.println("Now you are just being silly. Only Numbers allowed");
      years=input.nextDouble();

    }

    //Compute Investment Amount
    double future = amount * Math.pow((1 + interest), (years * 12));

    //Display Results
    System.out.println("Your future investment amount is " + future);

}

}