Visual Basic.NET How to Program (PDF)

636 Strings, Characters and Regular Expressions Chapter 15
22 string3 = New String(characterArray, 6, 3)
23 string4 = New String("C"c, 5)
24
25 output = "string1 = " & quotes & string1 & quotes & _
26 vbCrLf & "string2 = " & quotes & string2 & quotes & _
27 vbCrLf & "string3 = " & quotes & string3 & quotes & _
28 vbCrLf & "string4 = " & quotes & string4 & quotes
29
30 MessageBox.Show(output, "String Class Constructors", _
31 MessageBoxButtons.OK, MessageBoxIcon.Information)
32 End Sub ' Main
33
34 End Module ' modStringConstructor
Fig. 15.1 String constructors (part 2 of 2).
In line 11, we declare variable quotes and give it the value returned by function
ChrW when ChrW is passed a value of 34. The value passed to function ChrW is a Unicode
character code. Function ChrW returns as a Char data type the character that corresponds
to the specified Unicode character code. In this case, function ChrW returns a double quote
character ("). (To learn more about character codes, see Appendix F, Unicode.)
Lines 15–16 allocate Char array characterArray, which contains nine characters.
The c suffix that follows each String converts it to a character literal. We do this because
Option Strict prohibits the implicit conversion from type String to type Char.
Line 19 assigns literal string "Welcome to VB.NET Programming!" to String
reference originalString. Line 20 sets string1 to reference String literal
originalString.
Software Engineering Observation 15.1
In most cases, it is not necessary to make a copy of an existing String object. All String
objects are immutable—their character contents cannot be changed after they are created.
Also, if there are one or more references to a String object (or any object for that matter),
the object cannot be reclaimed by the garbage collector. 15.1
Line 21 assigns to string2 a new String object, using the String constructor
that takes a character array as an argument. The new String object contains a copy of the
characters in array characterArray.
Line 22 assigns to string3 a new String object, using the String constructor
that takes a Char array and two Integer arguments. The second argument specifies the
starting index position (the offset) from which characters in the array are copied. The third
argument specifies the number of characters (the count) to be copied from the specified
starting position in the array. The new String object contains a copy of the specified
characters in the array. If the specified offset or count indicates that the program should