This one is way way over my head

Question about the task

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Could someone please direct me to more information about this topic. The only thing I could find was decoder() method that was not working at all. Oracle is even more vague about this topic and writes in a language that is incomprehensible to me. I have no idea where even to begin with this task. Have I missed an important lesson on url parsing? If someone can direct me to a tutorial on this topic very much appreciated!

Read a URL from the console.
Display a space-delimited list of all the parameters (The parameters follow the "?" and are separated by "&", e.g. "lvl=15").
The URL contains at least 1 parameter.
The parameters must be displayed in the same order in which they are present in the URL.
If the obj parameter is present, pass its value to the relevant alert method.
alert(double value) - for numbers (fractional numbers have a decimal point)
alert(String value) - for strings
Note that the alert method must be called AFTER the list of all parameters is displayed.

Example 1

Input:
http://codegym.cc/alpha/index.html?lvl=15&view&name=Amigo

Output:
lvl view name

Example 2

Input:
http://codegym.cc/alpha/index.html?obj=3.14&name=Amigo

Output:
obj name double: 3.14

Requirements:

The program should read only one line from the keyboard.
The Solution class must not have static fields.
The program must display data on the screen in accordance with the task conditions.
The program should call the alert method with the double parameter if the obj parameter can be correctly converted to a double.
The program should call the alert method with the String parameter if the obj parameter CANNOT be correctly converted to a double.

package com.codegym.task.task15.task1527; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.UnsupportedEncodingException; import java.net.URLDecoder; import java.nio.charset.StandardCharsets; /* Request parser */ public class Solution { public static void main(String[] args) { //write your code here BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String url = ""; try { url = reader.readLine(); System.out.println(URLDecoder.decode(url, "UTF-8")); reader.close(); } catch (IOException e){} } public static void alert(double value) { System.out.println("double: " + value); } public static void alert(String value) { System.out.println("String: " + value); } }

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Level 25 , United States, United States

13 April 2020, 09:15

I'm not sure if they've mentioned much of it yet, if any, but a solution I used (I believe I've seen other posts on here using this solution as well), is to either match it using Regular expressions (can get really complicated fast, but extremely powerful and definitely a useful subject to learn) or to use splits. The idea is you split the url in half at the "?", leaving you with 2 strings. The first being the url (http://codegym.cc/alpha/index.html), and the parameters/values (lvl=15&view&name=amigo). From there, you take the 2nd string with the parameters/values and split that at "&", giving you an array containing [lvl=15, view, name=amigo]. Once again, you split if there is an = sign to separate parameter names from their values and store the parameter names in a list. You also need to check for the "obj" parameter, and store its value if it is present.

Level 25 , United States, United States

13 April 2020, 09:15

solution

Here is some code to give you an idea:

String test = "http://codegym.cc/alpha/index.html?lvl=15&view&name=Amigo";
        String test2 = "http://codegym.cc/alpha/index.html?obj=3.14&name=Amigo";

        List<String> parameters = new ArrayList<String>();
        List<String> parametersValue = new ArrayList<String>();

        String[] array = test2.split("\\?");
        // array = [ http://codegym.cc/alpha/index.html, lvl=15&view&name=Amigo ]
        if(array.length == 2) {
            String toParse = array[1]; // lvl=15&view&name=Amigo
            String[] afterFirstParse = toParse.split("&");
            // afterFirstParse = [ lvl=15, view, name=amigo ]
            for(int i = 0; i < afterFirstParse.length; i++) {
                if(afterFirstParse[i].contains("=")) {
                    // If contains =, split (lvl=15 -> lvl, 15)
                    String[] parsed = afterFirstParse[i].split("=");
                    parameters.add(parsed[0]); // parameters holds parameter names, such as lvl, view, name.
                    if(parsed[0].equals("obj")) {
                        // If parameter name is obj, add its value to parametersValue to pass to alert function.
                        parametersValue.add(parsed[1]); // obj=3.14 -> 3.14
                    }
                } else {
                    // If it does not contain =, pass just the name. (such as view).
                    parameters.add(afterFirstParse[i]);
                }
            }
        } else {
            System.out.println("Malformed URL?");
        }
/*
        Final output:
        http://codegym.cc/alpha/index.html?lvl=15&view&name=Amigo
        parameters = [ lvl, view, name]
        parametersValue = [] / empty

        http://codegym.cc/alpha/index.html?obj=3.14&name=Amigo
        parameters = [ obj, name ]
        parametersValue = [ 3.14 ]
         */

Liliane Top

Level 17 , Amsterdam, Netherlands

28 April 2020, 19:59

You probably gave me the solution but I actually do NOT understand it at all. I do understand the first part 1) Split the URL into the address and parameters by creating a substring after ? 2) Split the parameters through '&' 3) split the parameters and its value through '=' 4) but how to know if you can convert one of the values into a double? instance of double doesn't work. 5) I have no idea why you check if the length of the parts equals 2. Big mystery. 6) Why are you parsing the parts? another mystery 7) Why are you using List? I am able to separate the parts but how to check if a part is a double to call the correct method? I hope you can help!

Level 25 , United States, United States

3 May 2020, 01:56

4. If you want to convert it into a double, you can call Double.parseDouble(value). 5. You actually don't NEED to for this exercise since we already know what the url is (http://codegym.cc/alpha/index.html?lvl=15&view&name=Amigo). But these exercises seem to throw some curveballs at you, so it's to make sure they don't try to throw you a URL that won't work for this exercise (such as "http://codegym.cc/alpha/index.html" with no parameters). The reason I check to make sure the length == 2 is to check that the url was split at the question mark. If my url is "http://codegym.cc/alpha/index.html" and I call split("\\?"), the array will only be a length of 1 ("http://codegym.cc/alpha/index.html") since there is no question mark to split. However, if I use url "http://codegym.cc/alpha/index.html?lvl=15&view&name=Amigo" and call split("\\?"), the array will be a length of 2 ("http://codegym.cc/alpha/index.html", "lvl=15&view&name=Amigo"). 6. I'm not clear on what you mean by parsing the parts? Are you referring to splitting by & and =? 7. If you are talking about lines 4 & 5, it's not necessary. You can just use ArrayList instead and it'll work the same. If you want to know why, you can read about the why here: https://stackoverflow.com/questions/12321177/arraylist-or-list-declaration-in-java

Liliane Top

Level 17 , Amsterdam, Netherlands

3 May 2020, 08:06

People like you make Codegym a very valuable place to learn Java! My questions 4) and 6) are related. I was not aware of the method Double.parseDouble(). That is the way to check if it's possibly a double. Cos as it doesn't work you move on to the next method with pm String. All clear now. Thanks again for educating me. Now I'm gonna read the link you mentioned. Today I planned to continue with the task of level 16. I hope you will continue educating me ;-).