Software Development

Setup to run a standalone EJB client and lookup to a Glassfish running EJB 3.1 stateless ejb.

• Install Glassfish plugin in Eclipse.
• Create a Enterprise Aplication Project using Glassfish server as the target runtime.
• Create a HelloWorld example:

@Remote
public interface HelloWorld {}

@Stateless
public class HelloWorldEjb implements HelloWorld {}

• Create a Application Client Project using Glassfish server as the target runtime.
• Add gf-client.jar to the project classpath. gf-client.jar is included on the glassfish plugin folder inside eclipse, or in the glassfish standalone installation.
• Create the plain java code as the following:

InitialContext ctx;
HelloWorld ejbRef = null;
try {
   ctx = new InitialContext();

   ejbRef = (HelloWorld) ctx.lookup("eu.pedrocardoso.HelloWorld");

   System.out.println(ejbRef.getMessage("Hello"));

} catch (NamingException e) {
   e.printStackTrace();
}

• Optionally we can give properties to the initial context:

Properties p = new Properties();
p.put("org.omg.CORBA.ORBInitialHost","localhost");
p.put("org.omg.CORBA.ORBInitialPort","3700");

Default Glassfish iiop port is 3700

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Just to share a presentation about good estimation.

Video and slides: http://www.infoq.com/presentations/Want-Better-Estimates-Stop-Estimating

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The results of my practice exams. Not included the mocks, questions that I did in several sites pointed by JavaRanch.

From OCP Java SE 6 Programmer Practice Exams book (more SCJP resources)

• Assessment Test 1 - 71%
• Assessment Test 1 - 29%
• Exam 1 - 35%
• Exam 2 - 50%
• Exam 3 - 42%
• Exam 4 - 58%
• ExamLab Diagnostic Exam - 65%
• Exam Lab Exam 1 - 59%
• LearnKey Master Exam 1 - 65%
• LearnKey Master Exam 1 - 70%
• Oracle online practice exam - 87%
• OCJP exam: 85% PASS

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• SCJP – Java Enums
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• SCJP – Java I/O
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Since 1st June the SCJP, now OCJP, the exam (Exam Number : 1Z0-851) have 60 questions, 150 minutes duration and you have to pass in 61% of the questions (37).

Seems that there are no drag and drop questions.

All answers here:

http://blogs.oracle.com/certification/entry/0596

From Oracle blog:

The exam objectives and the exam questions themselves did not change.

• For three Java exams, some lengthy (time-consuming) questions were removed & replaced with shorter (less time-consuming) questions. This was done in order to shorten the required exam time (to 150 minutes).
• Some interactive question types were removed from several Java and Solaris exams (including "matching" and "drag-and-drop" questions).

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• SCJP – Language fundamentals
• SCJP – Java Collections Cheat Sheet
• SCJP – Java Enums
• SCJP – New Java 6 features
• SCJP – Java I/O

• enum CoffeeSize { BIG, HUGE, OVERWHELMING };
  • CoffeeSize cs = CoffeeSize.BIG;
• enum CoffeeSize { BIG, HUGE, OVERWHELMING }; // <--semicolon  is optional here

• CoffeeSize.values()  // returns a Collection of CoffeeSize enums. A Collection, not an array

• Syntax example of a enum usage

public class WeatherTest {
   static Weather w;
   public static void main(String[] args) {
       System.out.print(w.RAINY.count + " " + w.Sunny.count + " ");
   }
}
enum Weather {
   RAINY, Sunny;
   int count = 0;
   Weather() {
      System.out.print("c ");
      count++;
   }
}

• All of an enum’s values are initialized at the same time, and an enum’s variables are treated as if they were instance variables, not static variables

• Enum declaration
  • Can declaring an enum outside a class
  • Can declaring an enum inside a class
  • Cannot declare enums in methods

• enum really is a special kind of class
  • You can add constructors, instance variables, methods,
  • and something really strange known as a constant specific class body.

• Constant specific class body: looks like an anonymous inner class for one enum value
  • OVERWHELMING(16) { body: methods override }

• == or equals on enums values evaluates true in both cases.
• The member variables declared inside an enum is by default static.

• You can NEVER invoke an enum constructor directly
  • The enum constructor is invoked automatically. For example, BIG(8) invokes the CoffeeSize(int) constructor.
• You can define more than one argument to the constructor, and
  • you can overload the enum constructors, just as you can overload a normal class constructor.

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Main classes and methods

Console

•  System.console()

• readLine(String format, String args) - returns a string with the line read.

• Invoking close() on the objects returned by the reader() and the writer() will not close the underlying stream of those objects.
• methods doesn't throw checked exceptions
• console.reader().close();  //close method throws IOException
• Invoking close() on the objects returned by the reader() and the writer() will not close the underlying stream of those objects.

• Scanner.nextLong returns the next long, but doesn't advance to the the input if it's not a long.

NavigableSet / NavigableMap

• It's a new interface (extends SortedSet / sorted Map) for Java 6.

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Some diagrams and tables in this post from SCJP Sun Certified Programmer for Java 6 book.

Don't forget to study the io objects constructors:

• dir.list()  //returns a new String[] with a list of all file and folders in the dir directory;

• new PrintWriter("myFile.txt");
  • When the constructor is called, it truncates the existing file to zero size.
• File f1 = new File("sub1");;     f1.mkdir();
  • if the file exists doesn't throw a exception. It returns a boolean indicating whether or not a new
    directory was made
  • Most of interfaces of java.io returns boolean to indicate error or success.
• File f3 = new File(f1, "sub3");;   PrintWriter pw = new PrintWriter(f3);
  • Creates a empty file, on the f1 folder, but only during the PrintWriter constructor.
• f.renameTo() method takes only anothe File as arg, not a string.

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• SCJP – Java Enums
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This is the title of an article on InfoWorld, that list the programming languages that are gaining more programmers.

1. Python
2. Ruby
3. Matlab
4. Javascript
5. R
6. Erlang
7. Cobol
8. CUDA extensions

The link to Google trends to compare those languages references on the web.

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Summary
Two of ThoughtWorks’ finest, Martin Fowler and Jez Humble, talk about the notion of Continuous Delivery, which enables organizations to build software that is production ready at all times. To do this, enterprises automate the build, deployment, and testing process, and improve collaboration between developers, testers, and operations. The duo discusses a variety of related issues.

Jez Humble is the product manager for the Go product at ThoughtWorks Studios and is co-author of “Continuous Delivery: Reliable Software Releases through Build, Test, and Deployment Automation.” Martin Fowler an author, speaker, and pundit on the topic of software development. He is chief scientist at ThoughtWorks and has written six books on software development.

Watch the interview here:

http://www.infoq.com/interviews/jez-humble-martin-fowler-cd

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Dont forget

• wait, notify or notifyAll must have the this object lock. So look if they are in a syncrhonized method

• To analyze synchronized method issues, don't forget to verify if the threads are being created in same runnable object. If don't the synchronized methods locks will be distinct.

• public void run() - is the signature of the method that must be extended to implement Runnable or to extend Thread

• JVM exit after all the non demons threads created by the application complete, or when a thread executes System.exit().
  • if a main thread exits or if it throws a runtime exception, the child threads proceeds without any problem.

• isAlive() - tests if this thread is alive. A thread is alive if it has been started and has not yet died.
• If the thread doesn't own a lock on the object, and if we try to wait on this object, an IllegalMonitorStateException is thrown at runtime.
• If a thread is waiting on another thread, and if those thread finishes the main thread is released without any problem.
• synchronized block should be defined on an object: synchronized(this) {}
• Thread.sleep causes the currently executing thread to sleep, even if called on a thread instance, not on the thread refereed in the code
• Priority 1 is low priority, 5 is normal, 10 is maximum prioprity
• interrupt and isInterrupted are Thread methods

• The small execution block (means: don't allow to change running thread) - is per bytecode line, not by intermediate expression. To be confirmed

• to a thread call wait, notify or notifyAll on a obj, the thread must own the lock for those obj.
• Thread.sleep - don't release the lock
• wait releases the lock

Synchronized  methods

• public static SafeDeposit getInstance(int code) {} , with a private static instance and a private constructor
  • does not guarantees only one instance, because the getinstance is not synchronized

• A class to be thread safe, the variables need to be private, and the get and set methods need to be synchronized

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