Computer Science Java: My program is not running. In addition I am fully sure I did this correctly. I need help.

What error message are you getting?

Hi Felix

I will answer the question a):

I try to recreate your code and it runs in my IDE but your formula to calculate Future Value is wrong. This is my correction:

public static double getFutureValue(int investment, double interestRate, int year){

        //return Math.pow(investment * (1 + interestRate), year);<--this is worng since it calculate(invest*(1+interest))^year
          return investment * Math.pow((1+interestRate), year);//<- this is how you should calculate
    }

I hope this can help a little. PS: I failed to see why you need to import java.lang.* and java.io.* , since as far as I know you only need to import the Scanner's package which is the java.util.Scanner. Well it might just me. Forgive my lack of knowledge

As for the question b:

I have recreate and your code in my IDE, please note since I am only testing your code I directly put it in Main class and main method:

package com.teamtreehouse;

import java.util.Scanner;


public class Main {

    public static void main(String[] args) {
    // write your code here

        Scanner in = new Scanner(System.in);
        System.out.println("Enter number of websites: ");
        int n = in.nextInt();
        for(int i = 0; i < n; i++){
            System.out.println("Enter the URL of the websites");
            String s = in.next();
            //String pattern = "[wW]{3}.[a-zA-Z0-9+&@#/%?=~_|!.,;]*(.[cC][oO][mM]|.[eE][dD][uU])";<-you don't need this

             if(s.matches("[wW]{3}.[a-zA-Z0-9+&@#/%?=~_|!.,;-]*(.[cC][oO][mM]|.[eE][dD][uU])")){//<-this how you should use String.matches(regex) method

                String[] a = s.split("[wW]{3}.");

                String[] b = a[1].split(".[cC][oO][mM]|.[eE][dD][uU]");//<- this is the correct regex
                System.out.println("The name of the website is '" + b[0] + "'");
            }
            else{
                System.out.println("You have entered invalid URL");//<-- I changed this
            }
        }
        in.close();
    }
}

First thing first since I am using Main class I declared Scanner as new object not passed argument. Then the most important point here is when you put s.matches(regex) you need to define the regex inside literally (at least in my IDE it is) that is why your code failed to read your patterns (maybe).

If you insist to declare the regex pattern in separate variable and since you already imported java.util.regex.*;, you must declare the regex not the String. Like this:

 System.out.println("Enter the URL of the websites");
 String s = in.next();
 Pattern pattern = Pattern.compile("[wW]{3}.[a-zA-Z0-9+&@#/%?=~-_|!.,;]*(.[cC][oO][mM]|.[eE][dD][uU])");
 Matcher matcher = pattern.matcher(s);
if(matcher.matches()){
//and so on...
}

Then in your pattern regex I add '-' character since some website (although not recommended) can put it in their address.

The most important point here let's start from the most obvious: why do you put println("Please enter URL"); in the **else statement? You do not provide any loop when the user input invalid URL. It is more appropriate since you terminate the process when the users input invalid URL is to give them message You have entered invalid URL

Okay next point: from what I can read from your code is you want to split the URL or most likely host name address from for instance www.google,com or www.ocw.mit.edu to google and ocw.mit respectively.

In order to do that your regex in the ** String[] b = a[1].split(".[cC][oO][mM].[eE][dD][uU]");** is incorrect. If you keep using that regex the it will return google.com and ocw.mit,edu rather the intended format.

You need to add OR pattern | between them. That is what I did in my code upstairs.

I hope this can help a little. Any other inputs are welcomed. Please forgive my lack of knowledge in regex and coding I try my best to give the most useful answer possible.