Cristina's Java Programming Blog: 2016

Thursday, 12 May 2016

Java67: Difference between Error vs Exception in Java - In...

Java67: Difference between Error vs Exception in Java - In...: Both Error and Exception are derived from java.lang.Throwable in Java but main difference between Error and Exception is kind of error ...

Friday, 29 April 2016

Order in Initialization

Do you know what the following piece of code will print?

	class MyClass {

	MyClass() {
	System.out.println("MyClass");
	}

	MyClass(String id) {
	System.out.println("MyClass " + id);
	}
	}

	class Parent {
	// static String id = "Parent";
	// MyClass instance1 = new MyClass(id);
	MyClass instance1 = new MyClass();

	Parent() {
	System.out.println("Parent");
	}
	}

	public class Test extends Parent {
	// static String id = "Test";
	// MyClass instance2 = new MyClass(id);
	MyClass instance2 = new MyClass();

	Test(String name) {
	System.out.println("Test");
	}

	public static void main(String[] args) {
	new Test("Cristina");
	}
	}

view raw TestInitialization(OrderOfConstructorCalls).java hosted with ❤ by GitHub

The answer is:

MyClass
Parent
MyClass
Test

Now can you tell which instance (instance1 or instance2) prints the first "MyClass" string?

Uncomment the commented lines and see for yourself!

http://stackoverflow.com/questions/14805547/are-fields-initialized-before-constructor-code-is-run-in-java

http://stackoverflow.com/questions/17806342/order-of-constructor-calls-in-multilevel-inheritance-in-java

Tuesday, 26 April 2016

Java EE Servlets

Introduction

I've been taking a short break before moving on to new challenges. With this occasion I'm tidying several older personal projects. Among these, my Haiku Gallery.

I resumed the review from watching again "Intro to Java. Unit 14. Intro to Java EE. GlassFish. Servlets." by Yakov Fain:

After reading Lesson 26 of Java Programming 24-Hour Trainer I wrote the vote servlet, adapted the client side of my application, packed everything in a WAR file using Eclipse IDE, and uploaded the archive to the Azure Cloud. As illustrated below.

The Client Side of VoteMyHaiku App

	<div>

	<h2>Windy Afternoon</h2>

	<p>Windy afternoon</p>
	<p>Your smile</p>
	<p>On a stranger's face</p>

	<form action=http://votemyhaiku.azurewebsites.net/VoteMyHaiku/vote method=Get>
	<input type=Submit name="smile" value="Like" class="my_button"/>
	</form>

	</div>

view raw WindyAfternoon.html hosted with ❤ by GitHub

The Servlet

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

	PrintWriter out = response.getWriter();
	String button1 = request.getParameter("smile");
	String button2 = request.getParameter("wait");

	if (button1 != null) {
	out.println("<html><body>");
	out.println("<h1>Smile!!!</h1>");
	out.println("</body></html>");
	}
	else if (button2 != null){
	out.println("<html><body>");
	out.println("<h1>Wait!</h1>");
	out.println("</body></html>");
	}

	}

view raw VoteServerServlet.java hosted with ❤ by GitHub

Vote My Haiku in the Azure Cloud:

http://votemyhaiku.azurewebsites.net/

Conclusions

1. I love Visual Studio Online "Monaco"!
2. Adam Bien is right: Java EE is easier than Javascript.

Homework (to self)

1. Warming up: Respond with beautiful HTML from the Vote Server Servlet.
2. Advanced: Persist votes in an SQL database. Re-order haiku pieces dynamically, based on voting results, and create a 'Top 3' section on the page.

Friday, 1 April 2016

Angular 2 Random Quote Generator, Step 1

I started coding freeCodeCamp's project titled 'Build a Random Quote Machine'.

Here's the first iteration:

	// import does not work in Codepen
	// using const instead
	const {Component, Inject} = ng.core;
	const {bootstrap} = ng.platform.browser;
	const {HTTP_PROVIDERS, Http, Response} = ng.http;

	@Component({
	selector: 'my-app',
	template: '<h1>{{ quote }}</h1>'
	})

	class QuoteComponent {
	quote: string;
	constructor(@Inject(Http) http) {
	http.get('http://cfierbin.github.io/assets/data/myQuotes.json')
	.subscribe((response: Response) => this.quote = response.text());
	}
	}
	bootstrap(QuoteComponent, [HTTP_PROVIDERS]);

view raw quotesStep1.js hosted with ❤ by GitHub

My textbook for learning Angular 2 is Angular 2 Development with TypeScript, by Yakov Fain and Anton Moiseev.

P.S. Today is April Fool's Day. Stay foolish! (Steve Jobs)

References

Saturday, 19 March 2016

Collections and Multithreading

Saturday, 27 February 2016

Java Enumerations

	package enums;

	enum CardTypes {
	CLUBS, // ♣
	DIAMONDS,//♦
	HEARTS, //♥
	SPADES // ♠
	}

	public class playingCards {

	public static void main(String args[]){

	CardTypes myCard = CardTypes.CLUBS;

	System.out.println("Your card is " + CardTypes.CLUBS);

	}

	}