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.