Cristina's Java Programming Blog: April 2016

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

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)

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