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26 Cards in this Set
- Front
- Back
what are value types?
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contain their data directly.
on assignment data is copied from one variable to the other and stored in two different locations on the stack. They are objects with methods. ex ToString. Derived from System.Object |
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name three general value types.
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1. built in types (numeric boolean etc..)
2. user defined types 3. enumerations |
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name some built in numeric types
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SByte/sbyte -128 to 127 1 byte
Byte/byte 0 to 255 1 Short/short -32768 to 32767 2 Integer/int -2147483648 to 42147483647 Uinteger/uint o to 4294967295 4 Long/long 8 Single/float 4 Double/double 8 Decimal/decimal 16 |
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name the built in types that are optimized
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Integer/int
Uinteger/uint Double/double |
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name some built in value types that are non-numeric
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Char/char 2 bytes
Boolean/bool 1 byte IntPtr platform Date/date 8 bytes |
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How to declare value types
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Dim b as Boolean = False
bool b = false |
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What type of constructors do value tyes have?
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Implicit constructors
so just declare and they are automatically instantiated. |
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Which .net language is not case sensitive?
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vb.net
C# is case sensitive |
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How do you determine if a variable has been assigned to a value?
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Declare is as nullable then use .hasValue
Dim b as Nullable(Of Boolean) = nothing Nullable<bool> b = null; or bool? b = null; If b.HasValue Then .. b.Value i |
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How do you create user-defined types (structures) ?
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Structure Cycle
Dim _val, _min, _max as Integer Public Sub New(ByVal min as integer, ByVal max as Integer) _val = min : _min= min : _max = max End Sub Public Property Value() as Integer Get return _val End Get Set (ByVal value as Integer) if value > _max then me.Value = value .... end Set End Property Public Overrides Function ToString() as String return value.ToString End Function |
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Difference between struct and class
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Structure ->Class
class is allocated on the managed heap rather than as X bytes on the stack ( 4 for each private integer field) and assignments between variables results in both pointing to same instance. Stuctures are more effecient |
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When should you use a structure over a class?
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when a structure type can meet the following:
represents a single value logically has an instance size less than 16 bytes is not frequently changed after creation is not cast to a reference type. |
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What are enumerations?
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Enumerations related symbols that have fixed values.
often used to provide a list of choices to user Ex: Enum Titles Mr Mrs Miss End Enum enum Titles { Mr, Ms, Mrs, Dr}; |
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How are enumerations stored and outputed
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Stored as integer
Outputed as string Dim t as Titles = Titles.Dr Console.WriteLine("{0}.", t) 'dislplays "Dr." |
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what are reference types?
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reference types store addresses of data (pointer) stored in heap.
assigning on ref to another will create 2 ref pointing to same data. |
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how is garbage collection triggered?
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automatically by runtime or by callig GC.Collect
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what are some built in reference types?
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system.object
system.string system.text.stringbuilder system.array system.io.stream system.exception |
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are system.strings mutable?
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no. they are immutable any change to the string causes the runtime to create a new string.
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name some methods of system.string
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replace
concat join format |
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how do you create mutable strings?
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use stringbuilder class
creates 16 byte buffer and grows as needed. |
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how to use stringbuilder ?
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dim sb as new system.text.stringbuilder(30)
sb.append("x") +or & equality inequality assignment |
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how do you create and sort an array?
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dim ar() as integer = {3,1,2}
array.sort(ar) console.writelie ("{0},{1}", ar(0),ar(1)) |
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name some common stream types?
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FileStream
MemoryStream StreamReader StreamWriter |
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code reading and writing to a file.
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dim sw as streamwriter = new streamwriter("x.txt")
sw.writeline("hi") sw.close dim sr as streamreader = new streamreader("x.txt") console.writeline(sr.readtoend) sr.close |
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how to handle exceptions
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try
dim x as int ... catch ex as Exception console.writeline(ex.message) end try |
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how to filter exceptions
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try
... catch ex as system.io.filenotfoudexception ... catch ex as system.unauthorizedaccessexcetion .... catch ex as exception .... end try |