- Special Case pattern bv‡gI cwiwPZ| Generally Null Object GKwU Subclass.
- Particular case mg~‡n Bnv special behavior provide Ki‡e i.e. null object return Ki‡e|
- hLb user GKwU class Gi valid instance specify Ki‡Z bv Pvq wKsev bv cv‡i Ges null reference pass Ki‡Z bv Pvq ZLb Bnv useful
- Null object Gi role n‡jv Bnv null reference ‡K replace K‡i Ges same interface implement Ki‡e wKš‘ †Kvb behavior _vK‡e bv|
Client-- requires a collaborator.
AbstractObject-- declares the interface for Client’s collaborator
- implements default behavior for the interface common to all classes, as appropriate
<strong>RealObject</strong>-- defines a concrete subclass of AbstractObject whose instances provide useful behavior that Client expects
<strong>NullObject</strong>-- provides an interface identical to AbstractObject’s so that a null object can be substituted for a real object
- implements its interface to do nothing. What exactly it means to do nothing depends on what sort of behavior Client is expecting
- when there is more than one way to do nothing, more than one NullObject class may be required
Code Example
- ProductService class Gi data cache Ki‡Z bv PvB‡j wKfv‡e Null Object pattern use Ki‡Z n‡e Zv wb‡¤œ †`Lv‡bv n‡jv-
- Project G GKwU new class Add Kwi Ges Dnvi name w`B NullObjectCache Ges Dnvi definition wb¤œiƒc-
public class NullObjectCache :
ICacheStorage
{
public void Remove(string key)
{
// Do
nothing
}
public void Store(string key, object
data)
{
// Do
nothing
}
public T Retrieve<T>(string
storageKey)
{
return
default(T);
}
}
- Gevi NullObjectCache ‡K ProductService G passed Kiv hv‡e|
- hLbB data cache Ki‡Z n‡e ZLb Bnv wKQzB Ki‡e bv Ges memgq ProductService G null return Ki‡e (G‡ÿ‡Î ensure Ki‡e †Kvb data cached n‡e bv|)
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