This time around, I’ll explain a very important object-oriented (OO) concept and some neat things you can do with a string in C# using a new type of object: StringBuilder.

If you haven’t read the last couple of TechTips, here’s what I’ve talked about: I introduced strings as a slightly different data type (a complex one, when compared to the simple data type presented before) and showed how to extract characters from it using a method called “substring.” Substring is very similar to an RPG BIF, but it’s a part of the string object, not a standalone function. Strings are objects and have “internal BIFs,” called “methods.” Some are similar to the RPG BIFs you know; others are something totally different.

Now that you’re all caught up, let’s continue to explore the weird world of strings.

Strings are not only weird because they have methods and properties. Strings are objects, and these characteristics come with the territory. What makes them weird is something else, which I’ll talk about later in this TechTip.

Let’s fire up Visual Studio and open the project we’ve been working on for the last few TechTips of this series. I’ll show you a few more things about strings.

Let’s start by defining a new variable, below the int myStringLen = aTextTest.Length; line. You can either type or copy+paste the following line:

string aDifferentString = "Learning C# is fun!";

Now go to this line:

Console.WriteLine("The total length of the string is " + myStringLen);

And type or copy+paste the following lines just below it:

// Inserting text on an existing string, just for output

Console.WriteLine("Using the Insert method to add some text results in: " + aDifferentString.Insert(15, "easy and "));

// But it doesn't affect the original string

Console.WriteLine("But the original string remains untouched: " + aDifferentString);

Let’s analyze this code line by line. If you want to access a specific position of a string, it’s better to use brackets and indicate the zero-based index of that position (yup, strings behave like zero-based index arrays in C#), as shown on the first line of code.

Now for the promised string weirdness du jour. Unlike RPG’s BIFs, most methods don’t change the original object’s value; they return a new value instead. For instance, the ToUpper() method shown a couple of TechTips ago didn’t change the aTextTest variable value.

Similarly, the Insert method shown on the second line of code (note that I’m ignoring the comment lines, which are shown in green) inserts a piece of text at the specified position and produces a new object. In other words, a temporary string, without a name, is returned by the Insert, inside the Console.WriteLine method, and doesn’t affect the value of the original aDifferentString object.

This is a very important OO notion: even though methods are part of objects, most methods work like functions in the sense that they output a value, but they don’t change the original object’s value. But what if you want to change the original value’s object? It’s simple; just assign the new value, transformed by the chosen method, to the original object, like this:

// Now let's change the value, by assigning the function output to the original variable

aDifferentString = aDifferentString.Insert(15, "easy and ");

Console.WriteLine("Now aDifferentString has a different value: " + aDifferentString);

There are some important tips about performance regarding strings that I have to mention. First of all, if you want to access a specific character within a string, don’t use the substring method; use the positional access shown above, because it’s much, much faster that the substring method. Second, because of the way strings are defined internally in C# (strings are immutable objects in C#, and I’ll explain that in a moment), they are not suitable for heavy manipulation. If you need to update a long string’s value intensively, use a StringBuilder object instead.

Before I show you how to define and use a StringBuilder object, let me just explain what “immutable objects” are. Every time you use one of the methods of a string object, you create a new string object in memory, which requires a new allocation of space for that new object. In situations where you need to perform repeated modifications to a string, such as concatenations, insertions, or text replacement operations, the overhead associated with creating a new string object can be costly.

The StringBuilder class can be used when you want to modify a string without creating a new object in memory. For example, using the StringBuilder class can boost performance when concatenating many strings together in a loop or modifying a long string systematically. Let’s take our aDifferentString object and use it to define a new StringBuilder object. Insert the lines below just after the last line of code you wrote:

// Manipulating strings with StringBuilder

// Start by creating a new StringBuilder object, based on an existing string

StringBuilder aDifferentStringOnSteroids = new StringBuilder(aDifferentString);

Console.WriteLine();

Console.WriteLine("aDifferentStringOnSteroids original value: "

                   + aDifferentStringOnSteroids);

Here, I’m defining a new variable, aDifferentStringOnSteroids, which is a StringBuilder, based on the aDifferentString object. Thus far, they have the exact same value. If I tried to concatenate some text to aDifferentString, a new “version” of the variable would be created in memory. In fact, any operation that modifies the string object, such as the ones I presented earlier, would take up some memory with “copies” of the string object. But a StringBuilder object doesn’t work like that; it changes the value in place, without creating a copy of the object.

Now let’s see what you can do with a StringBuilder object:

// Append some text

aDifferentStringOnSteroids.Append(" But sometimes is quirky...");

Console.WriteLine();

Console.WriteLine("aDifferentStringOnSteroids after the Append:\n"

                   + aDifferentStringOnSteroids);

// Insert some text

aDifferentStringOnSteroids.Insert(46, "very ");

Console.WriteLine();

Console.WriteLine("aDifferentStringOnSteroids after the Insert:\n"

                   + aDifferentStringOnSteroids);

// Replace some text

aDifferentStringOnSteroids.Replace("very", "extremely");

Console.WriteLine();

Console.WriteLine("aDifferentStringOnSteroids after the Replace:\n"

                   + aDifferentStringOnSteroids);

// Remove some text

aDifferentStringOnSteroids.Remove(28, 37);

Console.WriteLine();

Console.WriteLine("aDifferentStringOnSteroids after the Remove:\n"

                   + aDifferentStringOnSteroids);

When you run this code, it’ll produce the following output:

Figure 1: Here’s our program’s current output.

Remember that I said most methods don’t change the original object’s value? Well, because of the way StringBuilder is rigged, its methods do the exact opposite. This serves to prove that you should always read the documentation before making the wrong assumption about how to use a method or an object type.

Just a few of notes about the code above: “\n” represents an ENTER character (line feed + carriage return, for the purists). The Append method is StringBuilder’s concatenation and the Insert method is similar to the string’s. Then Replace should be intuitive, and Remove is somewhat similar to the string’s Substring method, but instead of creating a copy of the piece of text, actually removes the characters. In this case, it removes 37 characters, starting on position 28 of aDifferentStringOnSteroids.

If I were to perform these operations using the original string variable, I’d use a lot more memory and the whole process would be slower. Perhaps not noticeably slower, because the text is not very long and it’s just a handful of operations, but definitively slower.

That’s all for now! The next TechTip will introduce arrays and lists. As usual, you can ask questions, make suggestions, and make corrections (yes, I’m only human and make mistakes) in the Comments sections below.

Rafael Victória-Pereira has more than 20 years of IBM i experience as a programmer, analyst, and manager. Over that period, he has been an active voice in the IBM i community, encouraging and helping programmers transition to ILE and free-format RPG. Rafael has written more than 100 technical articles about topics ranging from interfaces (the topic for his first book, Flexible Input, Dazzling Output with IBM i) to modern RPG and SQL in his popular RPG Academy and SQL 101 series on mcpressonline.com and in his books Evolve Your RPG Coding and SQL for IBM i: A Database Modernization Guide. Rafael writes in an easy-to-read, practical style that is highly popular with his audience of IBM technology professionals.

Rafael is the Deputy IT Director - Infrastructures and Services at the Luis Simões Group in Portugal. His areas of expertise include programming in the IBM i native languages (RPG, CL, and DB2 SQL) and in "modern" programming languages, such as Java, C#, and Python, as well as project management and consultancy.

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MC Press books written by Rafael Victória-Pereira available now on the MC Press Bookstore.

		Evolve Your RPG Coding: Move from OPM to ILE...and Beyond Transition to modern RPG programming with this step-by-step guide through ILE and free-format RPG, SQL, and modernization techniques. List Price $79.95 Now On Sale
		Flexible Input, Dazzling Output with IBM i Uncover easier, more flexible ways to get data into your system, plus some methods for exporting and presenting the vital business data it contains. List Price $79.95 Now On Sale
		SQL for IBM i: A Database Modernization Guide Learn how to use SQL’s capabilities to modernize and enhance your IBM i database. List Price $79.95 Now On Sale

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