Local meetup – AngularJS intro

Lately I’ve been toying with AngularJS and I wanted to share my findings in a short practical presentation. I will be building a small SPA (single page application) with AngularJS and run through the most commonly used directives and features of the framework.

If you are in Bucharest on 8th of December, after work (19:00) drop by and have a look :) The presentation will be in the ADCES group, the location being Electronic Arts (AFI Park 2).

Entrance is free, just register on this event either via Facebook or via Meetup. Hope to see you there :)

PS: Did I tell you that we’re having beers afterwards? ;)

Visual Studio smart replace

Let’s say you need to replace an expression in many files in Visual Studio with another expression. The case in question is replacing

nameof(someVariable)
to
"someVariable"

Sure you can try to replace

nameof(
to
"

but this will leave the double quote open and we don’t want this. Searching on the internetz and finding some stackoverflow solution and with the help of a second pair of eyes from a colleague we managed to find a solution like so:

Hit CTRL-SHIFT-H in Visual Studio and check “Use Regular Expressions”. Then select your scope, for example “Entire solution” and use the following expressions:

Find what:
nameof\(([a-zA-z]+)\)

Replace with:
"$1"

This will do the job. Let’s analyze the expressions a bit. The “Find what:” one, first. ‘nameof’ is the literal occurence of ‘nameof’. The first round bracket is preceded by backslash because we need to escape it. This is because the round bracket is used in the regular expressions syntax while in our case we need to literally find it. This was the ‘\(‘ part.

Now there is the ‘([a-zA-z]+)’ part. This has several sub-parts. The round brackets mean that the whole segment should be captured. We’ll later see why and what this is. Next, the square bracket part means that this should match any letter be it uppercase or lowercase (yes, I didn’t handle digits or underscores etc. which may be used in parameter/variable names, that is left as an exercise to the reader :P ). The plus sign means the square bracket part may occur multiple times. This means that a parameter/variable name may have more than one such character. Finally we close this part with the round bracket.

The final part in the “Find what:” expression is a literal closing round bracket which, again, is escaped by being prefixed with a backslash.

In the “Replace with:” expression, the captured part in the previous expression (what is enclosed in the regular-expression-syntax round brackets) is expressed as $1, as first numbered. Finally we enclose this in double quotes because that is what we need.

As for why I had to rollback from C# 6 nameof expression to a stringly-typed version, that’s a story for another time, I guess.

Cross-platform browser keyboard shortcuts

As of recently I began working on a Mac-book pro and I have to get used to a keyboard with different keys and different layout. One of the most used piece of software today is a browser. I routinely use Opera but there are still sites that don’t work well with it, although it uses pretty much the same rendering engine like Chrome.

I suspect these issues arise from the fact that Chrome tends to become the new IE 6 for many web developers (i.e. : write a page, test it in Chrome, it works, the rest of browsers doesn’t matter to me, continue to next page etc.).

I consider, just like Scott Hanselman, that using the keyboard is the most efficient way to command a computer (and not the mouse / touchpad) therefore I strive to use it to the max. However, switching from OS X to the Windows virtual machine back and forth can be confusing since there are different shortcuts. For example F5 in Windows refreshes the window while in OS X it doesn’t (be it because by default you have to press Fn and then F5 in order to send F5 otherwise a media function will be sent or because this key does not do this function).

Therefore I gathered a few useful shortcut keys that work in both Windows and OS X so I can use them. Many of them work across all major browsers (IE, Firefox, Chrome, Opera and Safari). Use Command (Cmd) key in OS X and Control (Ctrl) in Windows. I’ll include only the secondary key(s) in the table below since the primary key should be held down. I am planning to update this table several times.

Function Second key Internet Explorer Opera for Windows Opera for Mac Chrome for Windows Chrome for Mac
Quit (Close) app Q  x
Close tab (window) W  ✓
Refresh tab R  ✓
Open a new tab T  ✓
Open last closed tab SHIFT-T  ✓
View source U  ✓  x
Print page P  ✓
Select all page content A  ✓
Save current page to computer S  ✓
Add to favorites / bookmark D  ✓
Find in page F  ✓
Find again G  ✓
Show history H  ✓  x
View downloads J  ✓  x
Focus the address bar L  ✓
Undo Z  ✓
Cut X  ✓
Copy C  ✓
Paste V  ✓
Open a new window N  ✓
Open a new private window SHIFT-N  ✓

✓ = available
x = unavailable
[white_space] = not yet verified

(work in progress)

Dear readers, what other useful shortcuts is this table missing?

Quick trick : Copy file path

Are you in a command line prompt and you need the full path of the file as an argument? You don’t need to type all of the path manually, not even pre-complete it using TABs. Just navigate to the file.
Here comes the trick part : hold SHIFT while right-clicking it. The context menu will look like so :

SHIFT-right-click-copy-as-path-contextual-menu-command

I wrote before about the SHIFT-right click so this is somehow connected.

You will then have the full path of the file in the clipboard ready to be pasted wherever you need.

Hope this helps someone! :)

Overriding and overloading in Java and .NET – differences, changes and gotchas

Foraying even more in the fundamentals of Java (coming from a .NET background) I’ve come across some interesting things, along with changes in Java SE 5. But first let’s clear up a bit these two notions (overloading and overriding).

Overriding

Is a language feature that allows a subclass/inheriting class to have a method identical (we’ll later see a slight exception to this) to the one in the base class/superclass in every way except the implementation. That is, to have the same return type, the same name, same paramater types, same parameter order, just the code (and the parameter names) can differ.

This is by no means a definitive definition, Wikipedia, .NET CLS’s and JLS may very well differ slightly.

A typical C# overriding example (yes, I also dislike animal examples but they are so eaaaasyyyy to come up with) :

public class Dog 
{
    public virtual void MakeSound()
    {
         Console.WriteLine("Bark.");
    }
}

public class Hound : Dog
{
    public override void MakeSound()
    {
         Console.WriteLine("Wooofff!!!");
    }
}

Java developers unaware of the intricacies of C# will wonder what is that “virtual” thing. In C# all methods are “final” (sealed) by default unlike Java where methods are “virtual” (non-final / non-sealed) by default. This is a profound difference which we’ll discuss later. The “:” stands for “extends”. We’ll discuss the “override” keyword soon, also.

The equivalent piece of code in Java would look like :

public class Dog {
    public void makeSound() {
        System.out.println("Bark.");
    }
}

public class Hound extends Dog {
    public void makeSound() {
        System.out.println("Woofff!!!");
    }
}

Read more »

Numeric literals in Java 7 and in C#

In both Java and C# it’s quite easy to express integer numerical literals. You can use both decimal and hexadecimal base to represent the value. Only for the hexadecimal base you need to prefix the value with 0x. For decimal base values that exceed 2^31-1 you need to provide a suffix (typically L) specifying this fact so the compiler will treat it like a long integer value. C# also provides unsigned long values (U prefix). In both languages the casing of the suffix does not matter.

Java : (notice, there are no unsigned primitives in Java)

int i1 = 23; // integer, decimal
int h1 = 0x17; // integer, hexadecimal
long i2 = 12345678900L; // long integer (64 bit signed integer)

C# :

int i1 = 23;
int h1 = 0x17;
ulong u1 = 12345678900U;
long i2 = 12345678900L;

As you might have read in Beginning Java for .NET developers on slide 14, beginning in Java 7 you can also use two more features, that are not present in C# (at least at the time of this writing) :

Binary base :

int b1 = 0b11001010;

Underscores in literals (no matter which base) :

int b1 = 0b1100_1010;
long myCardNumber = 2315_2432_2111_1110;
int thousandsSeparated = 123_456_000;

The restrictions on the underscore placing is that you may not place it at the beginning of the value (prefix) or at the end (suffix). Also, for non-integer literals, you may not place it adjacent to the decimal separator.

For floating-point literals you must use the dot as decimal separator (if you need to specify a fraction, if not, you’re not required). You must use F for float-single-precision (32 bit) and D for float-double-precision (64 bit). Moreover in C# you have also the M suffix corresponding to the decimal (128 bit) value type.

C# :

float x1 = 0.001F;
double x2 = 12.33D;
decimal x3 = 111.2M;
float x4 = 33F;

Java :

float f1 = 0.001F;
double f2 = 12.31D;
float f3 = 123F;

Enum – comparison of Java and .NET

A useful feature added in Java 1.5 (also known as J2SE 5.0, 2004) is the enum. In .NET enums have been present since the very first version (2002, and as a beta since 2000) but the engineers at Sun managed to learn something from the shortcomings of the enums in .NET and provided more flexibility.

Let’s start with the simplest, the .NET implementation. In .NET all data types, including value types (equivalent of the primitive types) are part of the type hierarchy, being, indirectly inherited from System.Object (equiv. of java.lang.Object). The enums are just a specialization on top of exact numeric types, by default int (System.Int32). A typical declaration :

public enum Month
{
    January,
    February,
    March,
    April,
    May,
    June,
    July,
    August,
    September,
    October,
    November,
    December,
}

Notice that the compiler is forgiving and doesn’t complain that after the last element we forgot to not place a comma. It will also work, of course, if we don’t place a comma after the last element. Behind the scenes the compiler will generate a value-type inheriting from System.Enum that will have 12 constants. By default these constants we’ll be of type Int32 and their value, again, by default, will start from 0 and increase by 1 for each member. January will be 0 and December will be 11. Casts between the backing type (Int32 in this case) and the Months type will be allowed both at design time and at runtime.

You can also force individual values for each member

public enum Month
{
    January = 3,
    February = 33,
    March = 222,
    April = 14,
    May = 20,
    June = 23,
    July,
    August,
    September,
    October,
    November,
    December,
}

In this case January will be equal to 3, February 33, …, June 23, July 24 (not specified but after a value-specified member, the next member will be the last value + 1 if specific value is not present. You can even force things into a bad situation like so :

public enum Months
{
    January = 1,
    February,
    March,
    April,
    May,
    June,
    July = 1,
    August,
    September,
    October,
    November,
    December,
}

Guess what, not only this is completely valid, but there won’t be just two duplicate values (January and July being equal to themselves, and equal to 1) but also February will be 2, just like August and so on. Of course, this is not recommended. The compiler and the runtime will happily apply your stupid scheme but the humans will be confused. This excess of freedom is not to my liking but I can’t do much about it except counter-recommend it. Ideally you should not have to specify values for typical enums. Except for…
Read more »

Beware of primitive wrappers in Java

A .NET developer can be tricked into thinking that, for example, Integer is the same with int in Java. This is dangerous, in particular for a C# developer, because in C# System.Int32 is absolutely equivalent to int. “int” is just an alias.

In Java there are 8 primitive data types :

  • byte (this is equivalent to sbyte in C#)
  • short (just like short / Int16 in C#)
  • int (just like int / Int32 in C#)
  • long (equivalent to long / Int64)
  • float (similar to float / Single)
  • double (similar to double / Double)
  • boolean (equivalent to bool / Boolean)
  • char (equivalent to char / Char)

Now, these primitive types are not part of the Java Type System, as you might have seen in Beginning Java for .NET developers in the slides, at page 21. These primitives (“value types”) have reference-type peers that are typically spelled the same (except int/Integer, char/Character) and just have the first letter capitalized.

Just like you should avoid comparing strings with == in Java, you should avoid declaring variables and fields of the reference-type peers, unless for a good reason.
The main danger lies in the fact that being reference types and Java not having operator overloading (see Beginning Java for .NET developers, slide 15) comparing two instances with the == operator will compare the instances and not the values.

“Oh, but you’re wrong!”, some of you might say, “I’ve written code like this and it worked!”. Code like this :

public class Main {

    public static void main(String[] args) {
        Integer i1 = 23;
        Integer i2 = 23;

        System.out.println("i1 == i2 -> " + (i1 == i2));
    }
}

Yes, it does print

i1 == i2 -> true

It will work to values up to 127 inclusive. Just replace 23 with 128 (or higher) and see how things go. I’ll wait here.
Surprised? You shouldn’t be. This thing works because of a reason called integer caching (and there are ways to extend the interval on which it works – by default -128 up to 127 inclusive) but you shouldn’t rely on it.

Just use int where available or at least use the .intValue() method.

You might wonder what is the Integer (and the rest of the reference-type wrappers) there for? For a few things where they are needed. Once, because the generics in Java are lacking and you can’t define a generic type with primitive type(s) as type arguments. That’s right, you can’t have List. Scary? Yes, especially when coming from .NET where generics are not implemented with type erasure. So you need to say List and then watch out for reference comparison instead of value comparison, autoboxing performance loss and so on.

The other reason why you need these wrappers is because there is no nullable-types support in Java. So if you need to have a variable or a field that can store a primitive type but might also have to store a null then Integer will be better for you than int.

Just make sure you understand these implications and … be (type :P ) safe!

Avoid comparing strings with == in Java

While beginning development in Java, especially if coming from a .NET background (but not necessarily) you might do string comparison with == in Java. Don’t do it. It will compare the string instances and not their effective value.
You might even try it first to check if == really works, testing it in a wrong manner like so :

public static void main(String[] args) {

    String s1 = "Abc";
    String s2 = "Abc";

    System.out.println("s1 == s2 -> " + (s1 == s2));
}

This will output

s1 == s2 -> true

.. which might lead you to believe this works. This does return the correct value because of a feature present in Java and .NET called string interning (not specific to Java or .NET).

Try to obtain a string instance dynamically like concatenating two existing instances and see how things don’t work anymore :

public static void main(String[] args) {

    String s1 = "Abc";
    String s2 = "Abc";

    // new lines :
    String capitalA = "A";
    String bc = "bc";
    String s3 = capitalA + bc;

    System.out.println("s1 == s2 -> " + (s1 == s2));
    // new line :
    System.out.println("s1 == s3 -> " + (s1 == s3));
}
s1 == s2 -> true
s1 == s3 -> false

Weird, huh? That’s because at compile time there are four distinct strings generated : “Abc” (once, even if referred twice), “A” and “bc”. The “Abc” instance obtained by joining “A” and “bc” will be generated at runtime and, of course, it will be a different instance than the first “Abc” instance. That’s why the result of the == operator comparison will be false.
Read more »

Simulating C# ref parameter in Java

As I was saying a few posts ago (Beginning Java for .NET Developers), on the 8th slide, there are no ref and no out method parameter modifiers.

These are rarely used in .NET anyway so you can’t really complain of their lack in Java. Furthermore, some of their legitimate uses, such as the static TryParse methods on value types are not applicable in Java. Why? Because in Java the primitives (int, long, byte etc. – the equivalent of the basic value types in .NET) are not part of the type hierarchy and they have reference-type wrappers (Integer etc.) which would solve the issue of returning the result in case of ‘TryParse’ style of parsing. How’s that? It’s like :

public static Integer tryParseInt(String intString) {
    try {
        return Integer.parseInt(intString);
    } catch (NumberFormatException e) {
        return null;
    }
}

No need for a ‘out’ parameter or ‘ref’. But! Let’s try and simulate ‘ref’ using a generic class written this way :

public class Ref<T> {
    private T value;

    public Ref() {
    }

    public Ref(T value) {
        this.value = value;
    }

    public T getValue() {
        return value;
    }

    public void setValue(T value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return value == null ? null : value.toString();
    }
}

Read more »

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