[Java Tutorial #8] - How to create SP to Vests Converter Calculator...

Repository

https://github.com/dmlloyd/openjdk

What Will I Learn?

You will learn How to create GUI form for this aplication
You will learn API to convert SP to VEST
You will learn how to get data from user input and multiply it with the price from API URL
You will learn how to display last data to the form

Requirements

Basic knowledges about java programing
Basic Knowledges about API
Need to Install Netbeans for easy pratice

Difficulty

Basic

Tutorial Contents

In this tutorial, I will try to explain how to make a calculator application to convert steem power to vest. The user inputs the amount of steam power and the system will issue amounts in the vests. Here is what the app looks like:

Let's start the tutorial :

Open Netbeans IDE software and create new project. Choose Java Aplication and click next. Then Rename the project and click finish.
Add new jFrameForm in your Source Package
Click on panel component and drag it to the form
Add Label, TextField and Button on Panel, just follow the components on picture bellow :
We already have a form, Now open source and start to edit the code.
Create The method to get Data from URL. This method in java.net.* method. So before your start use this method import the package first

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.logging.Level;
import java.util.logging.Logger;

Then create a method to read url from web

public String getApi(String url) throws Exception{
        URL oracle=new URL(url);
        HttpURLConnection httpcon = (HttpURLConnection) oracle.openConnection();
        httpcon.addRequestProperty("User-Agent", "Mozilla/5.0");
        BufferedReader in = new BufferedReader(new InputStreamReader(httpcon.getInputStream()));
        String inputLine;
         while ((inputLine = in.readLine()) != null){
             return inputLine;
         }  
        in.close();
        return null;   
    }

Code	Explanation
`getApi()`	Method Name
`String url`	The Parameter
`throws Exception`	Some method to catch error
`URL oracle=new URL(url);`	Decrlarating new URL
`HttpURLConnection httpcon = (HttpURLConnection) oracle.openConnection();`	class initiation to get URL connection.
`httpcon.addRequestProperty("User-Agent", "Mozilla/5.0");`	Add browser property, Here I add Mozilla 5.-0
`BufferedReader in = new BufferedReader(new InputStreamReader(httpcon.getInputStream()));`	method Read input from http connection.
`return inputLine;`	return the output
`in.close();`	close input stream reader

Now create a method to count vests in Steem power

public void calc() throws Exception{
       String Data = getApi("https://uploadbeta.com/api/steemit/converter/?cached");
       JSONObject ObjData=new JSONObject(Data);
       vest.setText(""+Double.parseDouble(sp.getText())*ObjData.getDouble("sp_to_vests"));
    }

Code	Explanation
`calc()`	Method Name
`getApi`	we call the previous method to get Data from URL. and the parameter is URL from https://helloacm.com/tools/steemit/
`JSONObject ObjData=new JSONObject(Data);`	convert the result from string to JSON Object. Here we need use java-json library. Dowload it here : http://www.java2s.com/Code/Jar/j/Downloadjavajsonjar.htm . Extract and add to project Libraries. Then import it to your file, then import `org.json` package
`vests.setText`	setText method for vest convert result
`Double.parseDouble(sp.getText())`	get double value from user input
`ObjData.getDouble("sp_to_vests")`	get sp price in vests from object data API
`""+`	The Variable that will be set as text in componen, because the variabel type is double we need combine with a string. So I use ""+.

Call the calc() method in convert button. Open the aplication design form and double click on button. then add this code.

    private void convertActionPerformed(java.awt.event.ActionEvent evt) {                                        
        try {
            calc();
        } catch (Exception ex) {
            Logger.getLogger(calculator.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

save all code, and try to run the app
Finish, the aplication is running rightly. You can get the full code on my gist. The link is bellow

Curriculum

Proof of Work Done

https://gist.github.com/team2dev/a5f030cd6f5a78b460ca248786da0937

[Java Tutorial #8] - How to create SP to Vests Converter Calculator Aplication using Netbeans