I need to get rid of that switch statement. What is the Strategy Pattern?

I’m a big advocate of software maintainability and there is nothing better for that than applying well known patterns to improve the existing code. Each time I see long if..then..else constructs, or switch statements to drive logic, I think of how much better the code would be if we allow encapsulation and use one of my favorite behavioral pattern… => the Strategy Pattern.

StrategyPatternA Strategy is a plan of action designed to achieve a specific goal

This is what this pattern will do for you: “Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.” (Gang of Four);

Specifies a set of classes, each representing a potential behaviour. Switching between those classes changes the application behavior. (the Strategy). This behavior can be selected at runtime (using polymorphism) or design time. It captures the abstraction in an interface, bury implementation details in derived classes.

When we have a set of similar algorithms and its need to switch between them in different parts of the application. With Strategy Pattern is possible to avoid ifs and ease maintenance;

Now, how can we digest that in code, now that you got the gist of the problem and want a better solution than your case statements.

This example I’ll be showing is a pure academic exercise:

The problem to solve is given a string as an input, create a parsing algorithm(s) that given a text stream identifies if the text complies with the following patterns. Angle brackets should have an opening and closing bracket and curly brackets should also have an opening and closing bracket, no matter how many characters are in the middle. These algorithms must be tested for performance.

<<>>{}  True
<<{>>}  False
<<<>    False
<<erertjgrh>>{sgsdgf} True


Continue reading I need to get rid of that switch statement. What is the Strategy Pattern?

Java vs. C# access modifiers looked at by a C# programmer

I’m looking into the SCJP 6 as I don’t have hands on experience on Java projects (only academic apps).

I had bookmarked long time ago a great C# vs. Java comparison Dave Obasanjo made:

A COMPARISON OF MICROSOFT’S C# PROGRAMMING LANGUAGE TO SUN MICROSYSTEMS’ JAVA PROGRAMMING LANGUAGE



I noticed tonight that the member’s access modifiers could use some tuning and show:

C# access modifier

Java access modifier

private

private

public

public

internal

Default (package-private)

protected

N/A

internal protected

protected



In Java, a protected member can only be accessed through classes on the same package and through subclasses whether they are on the same package or not.

The protected modifier specifies that the member can only be accessed within its own package (as with package-private or default) and, in addition, by a subclass of its class in another package. Package + Kids access.

The default access modifier in Java happens when a class member has no modifier (the default is also known as package-private). This means the member is only accessible by a class defined within the package.

Adding an empty item to an IList collection at runtime.

How can I add a new empty item to a datasource (BindingSource) if the collection that it contains has objects of unknown type at design time:

if (dataSource.GetType() == typeof(BindingSource))
{
IEnumerator en = dataSource.GetEnumerator();
en.MoveNext();
Type t = en.Current.GetType();

object o = System.Activator.CreateInstance(t, false);

dataSource.Add(o);
}

where dataSource is of type IList.

This was a request to add an empty line to a windows forms combobox and to a listbox.

BindingSource can be bound to any of the following:

  • Object
  • System.Type
  • IEnumerable
  • ICollection
  • IList
  • IListSource
  • IBindingList
  • IBindingListView