[Java Tutorial #2] - How to create GUI aplication for displaying Live SBD price using Netbeans

Repository

https://github.com/dmlloyd/openjdk

What Will I Learn?

• You will learn How to get JSONdata from URL API
• You will learn how to split data and dislay ony the important data
• You will learn how to display result on GUI form

Requirements

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

Difficulty

• Basic

Tutorial Contents

In the previous tutorial, I've explained how to retrieve data from API URLs using JAVA programing. And on this occasion, I will continue the previous tutorial that is how to display data into GUI form on java application

Let's Start :

• Open Netbeans IDE software and create new project. Choose Java Aplication and click next. Then Rename the project and click finish

• Add a jFrameForm in your Source Package
  

• Open the java file on editor and start to code.
  

• Rename the Form
  

• Now Start to create a form. Just Follow the Components bellow :
  
  number : 1. jLabel
  number : 2. jLabel
  number : 3. jButton
  number : 4. jTextField
  

• We already have a form that contain a button and 4 jTextField. When the button clicked the data will display in jTextfied. Now open source and start to edit the code.
  

• Add getData method, This method i heve explained also in my previous tutorial. see here for more detail

public static String getData(String apiURL) {
        StringBuilder sb = new StringBuilder();
        URLConnection urlConn = null;
        InputStreamReader in = null;
        try {
            URL url = new URL(apiURL);
            urlConn = url.openConnection();
            if (urlConn != null)
                urlConn.setReadTimeout(60 * 1000);
            if (urlConn != null && urlConn.getInputStream() != null) {
                in = new InputStreamReader(urlConn.getInputStream(),Charset.defaultCharset());
                BufferedReader bufferedReader = new BufferedReader(in);
                if (bufferedReader != null) {
                    int lengthData;
                    while ((lengthData = bufferedReader.read()) != -1) {
                        sb.append((char) lengthData);
                    }
                    bufferedReader.close();
                }
            }
        in.close();
        } catch (IOException e) {
            throw new RuntimeException("Exception while calling URL:"+ apiURL, e);
        } 
        return sb.toString();
    }

Code	Explanation
StringBuilder sb = new StringBuilder(); URLConnection urlConn = null; InputStreamReader in = null;	This code to Instance Class Object.
if (urlConn != null) urlConn.setReadTimeout(60 * 1000);	set time for timeout when the URL is not empty
in = new InputStreamReader(urlConn.getInputStream(), Charset.defaultCharset());	restore the url as input stream
new BufferedReader(in);	Read the URL to grap or get Data
while ((lengthData = bufferedReader.read()) != -1) { sb.append((char) lengthData);}	Displaying data in while looping. this looping start from the index 0 until the end.

• As I have explained in previous tutorial, to get data from url and to use BufferedReader we should import net-URL, BufferedReader and IOException package.

import java.net.URL;
import java.net.URLConnection;
import java.nio.charset.Charset;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

• Create a method to display data on the form

void display() throws JSONException{
        final JSONObject obj = new JSONObject(getData("https://bittrex.com/api/v1.1/public/getmarketsummary?market=btc-sbd"));
        final JSONArray result=obj.getJSONArray("result");
        final int n = result.length();
        for (int i = 0; i < n; ++i) {
            final JSONObject person = result.getJSONObject(i);
            marketName.setText(person.getString("MarketName"));
            realTime.setText(person.getString("TimeStamp"));
            lastPrice.setText(BigDecimal.valueOf(person.getDouble("Last")).toString()+" BTC");
            highPrice.setText(BigDecimal.valueOf(person.getDouble("High")).toString()+" BTC");
            lowPrice.setText(BigDecimal.valueOf(person.getDouble("Low")).toString()+" BTC");
        }
    }

Code	Explanation
display()	Method Name
throws JSONException	This code to handle the error from JSON
final JSONArray result=obj.getJSONArray("result");	Get array value of result.
marketName.setText(person.getString("MarketName"));	this is the main code of this tutorial, it is to display the result on jTextField.
BigDecimal.valueOf(person.getDouble("High"))	Convert the Double to Decimal
toString()	because in jTextField component just can use String Type, so here we need to convert it to string.

• TO use JSONObject here we need to add 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.
  

import java.nio.charset.Charset;
import org.json.JSONException;
import org.json.JSONObject;
import org.json.JSONArray;

• The last one you need to import import java.math.BigDecimal; for BigDecimal package.

• The last step is call the display() method in jButton. Open the design and doble click on button.
  
  

• Add this code to call the display() method.

  try {
            display();   
        } catch (JSONException ex) {
            Logger.getLogger(form.class.getName()).log(Level.SEVERE, null, ex);
        }

The code above is for calling the display() method. We call this method in try and catch to handle the error.

• Finally, Save and try to run the project.
  
• Then click the check it button on the form. And you will see the data will display rightly.
  

Curriculum

[Java Tutorial] - How to create some java aplication to display Live SBD price from bittrex API using Netbeans

Proof of Work Done

https://gist.github.com/team2dev/bcac8e443d3d69de7803cc503d55d32e