State and FlyWeight patterns

Question

Can anybody share example of using state pattern with flyweight pattern (flyweight pattern is for creating state objects to save memory)?

UPDATE: How to use a combination of state and fw patterns?

Answer 1

Autoboxing uses the flyweight pattern to minimise object creation (for small values of Integer)

e.g. for Boolean and Byte all possible values are cached.

Java uses states for many components, however a state machine also includes functionality switched by state.

Here is an example I wrote using enum http://vanillajava.blogspot.com/2011/06/java-secret-using-enum-as-state-machine.html

Answer 2

I usually use state pattern to avoid conditional statements.

instead of using:

switch (state)
{
    case ParserState.BeforeMethod:
        //do some processing
        break;
    case ParserState.InMethod:
        //do some processing
        break;
}

I can just write:

currentState = currentState.process(context);

A sample class can look like

public class SomeClass : ParserState
{
    public ParserState process(IParserContext context)
    {
       //do some proceccing

       if (m_completed)
           return new SomeOtherState();

       return this;
    }

}

i.e. The logic is moved to small classes which are used to handle a specific state. So you get two things:

• Smaller classes with clear responsibilities
• Less conditional statements = more readable code.