1. Chengyu Sun California State University, Los Angeles
CS4540 Special Topics in Web Development C# for Java Programmers: Exceptions and Collections
Chengyu Sun
California State University, Los Angeles

2. Exception Handling Exception handling is mostly like in Java
No checked exception in C# (Yay!)
static void FutureFeature()
{throw new NotImplementedException(); }
static void Main(string[] args) {
try
{ FutureFeature(); }
catch (NotImplementedException e)
{ Console.WriteLine(e.Message); }
finally
{ Console.WriteLine("Done!"); }

3. What's Inside an Exception
Important properties in Exception
Message
StackTrace
TargetSite: can be used to obtain information about the method that threw the exception
Data: additional data (a collection of key-value pairs) associated with the exception

4. Using Standard Exceptions
There is already a large collection of exceptions defined in the System namespace
Some exceptions for common programming problems

5. Creating A Custom Exception
Minimum for a custom exception
Inherit from Exception or ApplicationException class
Have a no-argument constructor
Have a constructor that takes a string message
Or, use the ex code snippet in Visual Studio

6. Common Collections in Java
Interface
Class
Characteristics
List
ArrayList, LinkedList
Ordered; allow duplicates
Set
HashSet, LinkedHashSet, TreeSet
Un-ordered or ordered in a specific way; no duplicates
Map
HashMap, LinkedHashMap, TreeMap
Key-Value pairs
Queue, Deque
PriorityQueue, Stack
Common data structures

7. Generics
Type Parameter
public class GenericList<T> {
public void Add(T input) { } }
var list = new GenericList<int>();
Type Argument
Most commonly used to ensure all the elements in a collection is of the same type

8. Why Not Use Collection of Objects
Performance: has to convert back and forth between value types and reference types (aka boxing/unboxing)
Type safety
Cannot prevent different types of data getting into the same collection
Require explicit cast when accessing data

9. About Collections in C#
Non-generic collections are defined in System.Collections
Generic collections are defined in System.Collections.Generic

10. Common Collections in C#
Interface
Class
Characteristics
IList
List, LinkedList, SortedList
Ordered; allow duplicates
ISet
HashSet, SortedSet
Un-ordered or ordered in a specific way; no duplicates
IDictionary
Dictionary, SortedDictionary
Key-Value pairs
Queue, Stack
Common data structures

11. Example: English-Spanish Translator
Download the dictionary file from the Internet Dictionary Project
Read the file and store the dictionary in a Dictionary<string, List<string>>
Get an English word from input and displays its Spanish translations

12. Reading Text Files Using C#
Read the whole file using System.IO.File
Read one line at a time using System.IO.StreamReader

13. Element Access Add, Remove, RemoveAt, RemoveAll …
Dictionary.TryGetValue()
The "Item" property in Dictionary and List
More on indexer methods later

14. A Couple of Important Interfaces
IEnumerable<T>: foreach can be used on anything implementing this interface
ICollection<T>
Implements IEnumerable<T>
Count, Add, Remove, Contains

15. Readings
Pro C# 7: Chapter 7, 8, 9