What Are Generics?

Generics allow you to define type-safe classes without compromising type safety, performance, or productivity. You implement the server only once as a generic server, while at the same time you can declare and use it with any type. To do that, use the < and > brackets, enclosing a generic type parameter. For example, here is how you define and use a generic stack:

     public class Stack<T>     {        T[] m_Items;        public void Push(T item)        {...}        public T Pop( )        {...}     }     Stack<int> stack = new Stack<int>( );     stack.Push(1);     stack.Push(2);     int number = stack.Pop( ); 

Example D-2 shows the full implementation of the generic stack.

Example D-2. The generic stack

 public class Stack<T> {    const int DefaultSize = 100;    readonly int m_Size;    int m_StackPointer = 0;    T[] m_Items;    public Stack( ) : this(DefaultSize)    {}    public Stack(int size)    {       m_Size = size;       m_Items = new T[m_Size];    }    public void Push(T item)    {       if(m_StackPointer >= m_Size)       {          throw new StackOverflowException( );       }       m_Items[m_StackPointer] = item;       m_StackPointer++;    }    public T Pop( )    {       m_StackPointer--;       if(m_StackPointer >= 0)       {          return m_Items[m_StackPointer];       }       else       {          m_StackPointer = 0;          throw new InvalidOperationException("Cannot pop an empty stack");       }    } } 

Example D-2 is the same as Example D-1, except that in Example D-2 every use of object has been replaced with T, and the Stack is defined using the generic type parameter T:

     public class Stack<T>     {...} 

When you use the generic stack, you have to instruct the compiler which type to use instead of the generic type parameter T, both when you declare the variable and when you instantiate it:

     Stack<int> stack = new Stack<int>( ); 

The compiler and the runtime do the rest. All the methods (or properties) that accept or return a T will instead use the specified type (such as an integer).

T is the generic type parameter (or type parameter), while the generic type is Stack<T>.

The advantage of this programming model is that the internal algorithms and data manipulation remain the same, while the actual data type can change based on the way the client uses your server code.