Lesson 3: Compressing Streams

Compression - useful in real-world projects to save space or bandwidth. .NF supports 2 new stream classes that can compress data.

• GZIP & DEFLATE - 2 mthds inside .NF. Use industry-std compression algorithms. No intellectual-property issues.
• size limit - can compress upto 4GB of uncompressed data.
• said comp. mthds exposed by .NF as GZipStream() & DeflateStream().
• gzip or DEFLATE? - GZIP allows for headers for xtra info. Thus if internal use DefalteStream - slightly smaller but if distributing externally use GZIP.
• GZipStream() - allows comp.

How to Compress Data with a Compression Stream

• Compression streams don't write to a resource (e.g. a file, memory) - they write to other streams.
• typical scenario - read an existing file & write to a new compressed version of the file.
• GZipStream compStream = new GZipStream(destFile, CompressionMode.Compress) - a compression stream wraps the stream that contains (or will contain) compressed data.

lesson 2: Using Common Ref Types II

Understanding Readers & Writers

• TextReader/TextWriter - abstract classes fro mwhich StreamReader/Writer are derived.
• StringReader/Writer - to read/write to/fro in-memory strings.
• StringWriter uses a 'StringBuilder', so it is very efficient at creating ever larger strings.
• BinaryReader/BinaryWriter - for handling binary data to/from streams (i.e. binary files).
• long number = reader.ReadInt64(); byre[] bytes = reader.ReadBytes(4);...
• MemoryStream class - func. to create in-memory streams.
• When use MemoryStream? Do time-intensive work inthe MemoryStream and then open the dest. file, flush the data to it, and close the file quickly.
• BufferedStream - to wrap streams to improve performance by buffering reads & writes thro the stream. Writing out data to a stream directly does not perform very well. BufferStream wraps another stream object, to allow for writes to happen to a buffer. Only when the buffer is flushed does the data get pushed into the underlying stream.

lesson 2: Using Common Ref Types.

Ref Types Vs Value Types

• Ref variable - holds the address of data rather than the data itself.
• Assigning one ref. var to another - doesn't copy the data - merely creates 2nd copy of ref to same data.
• 2500 built-in ref types - everything NOT derived from System.ValueType

Strings/StringBuilder

• Immutable - cannot change - System.String.
• Avoid temporary strings - s = "a"; s+= "qwerty"; - 2 strings created, of which only the last will have a ref. 1st garbage collected. Avoid unnecessary garbage collection here by using String class's Concat(), Join() & Format() mthds. Or use StringBuilder class to create mutable strings.
• StringBuilder class - can span multiple stmts.

Create/Sort Arrays

• int[] ar = {3,1,2};
• Sort using static mthd - Array.Sort(ar);

Streams (System.IO.Stream)

• common type - means of reading from/writing to disk.
• StreamReader/StreamWriter - simplest - enable reading from/writing to txt files.
• sr.ReadToEnd();

Exceptions

• Catch block - skipped if no error encountered in try block.
• define own exceptions - derive from System.ApplicationException.
• Filtering Exceptions - mutiple catch blocks - runtime will only execute the 1st Catch block with a matching exception. THUS ORDER CATCH BLOCKS FROM MOST-SPECIFIC TO LEAST SPECIFIC.
• Finally{} - runs whether an exception occured or not.
• All code in try/catch blocks.