org.picocontainer.parameters
Class NullParameter

java.lang.Object
  org.picocontainer.parameters.AbstractParameter
      org.picocontainer.parameters.NullParameter

All Implemented Interfaces:

Serializable, Parameter

public class NullParameter
extends AbstractParameter
implements Serializable

Once in a great while, you actually want to pass in 'null' as an argument. Instead of bypassing the type checking mechanisms available in ConstantParameter, we provide a Special Type geared to marking nulls.

Author:

Michael Rimov

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.picocontainer.Parameter

Parameter.DelegateResolver, Parameter.NotResolved, Parameter.Resolver, Parameter.ValueResolver

Field Summary

static NullParameter

INSTANCE The one and only instance of null parameter.

Fields inherited from interface org.picocontainer.Parameter

DEFAULT, ZERO

Constructor Summary

protected

NullParameter() Only once instance of Null parameter needed.

Method Summary

void	accept(PicoVisitor visitor) Accepts a visitor for this Parameter.
protected boolean	isAssignable(Type expectedType) Nulls cannot be assigned to primitives.
Parameter.Resolver	resolve(PicoContainer container, ComponentAdapter<?> forAdapter, ComponentAdapter<?> injecteeAdapter, Type expectedType, NameBinding expectedNameBinding, boolean useNames, Annotation binding) Check if the Parameter can satisfy the expected type using the container.
void	verify(PicoContainer container, ComponentAdapter<?> adapter, Type expectedType, NameBinding expectedNameBinding, boolean useNames, Annotation binding) Verify that the Parameter can satisfy the expected type using the container

Methods inherited from class org.picocontainer.parameters.AbstractParameter

isResolvable, resolveInstance

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

INSTANCE

public static final NullParameter INSTANCE

The one and only instance of null parameter.

Constructor Detail

NullParameter

protected NullParameter()

Only once instance of Null parameter needed.

Method Detail

accept

public void accept(PicoVisitor visitor)

Accepts a visitor for this Parameter. The method is normally called by visiting a ComponentAdapter, that cascades the visitor also down to all its Parameters.

Specified by:

accept in interface Parameter

Parameters:

visitor - the visitor.

See Also:

Parameter.accept(org.picocontainer.PicoVisitor)

resolve

public Parameter.Resolver resolve(PicoContainer container,
                                  ComponentAdapter<?> forAdapter,
                                  ComponentAdapter<?> injecteeAdapter,
                                  Type expectedType,
                                  NameBinding expectedNameBinding,
                                  boolean useNames,
                                  Annotation binding)

Check if the Parameter can satisfy the expected type using the container.

Specified by:

resolve in interface Parameter

Parameters:

container - the container from which dependencies are resolved.

forAdapter - the ComponentAdapter that is asking for the instance

injecteeAdapter - the adapter to be injected into (null for N/A)

expectedType - the required type

expectedNameBinding - Expected parameter name

useNames - should use parameter names for disambiguation

binding - @return true if the component parameter can be resolved.

See Also:

Parameter.resolve(org.picocontainer.PicoContainer, org.picocontainer.ComponentAdapter, org.picocontainer.ComponentAdapter, java.lang.reflect.Type, org.picocontainer.NameBinding, boolean, java.lang.annotation.Annotation)

verify

public void verify(PicoContainer container,
                   ComponentAdapter<?> adapter,
                   Type expectedType,
                   NameBinding expectedNameBinding,
                   boolean useNames,
                   Annotation binding)

Verify that the Parameter can satisfy the expected type using the container

Specified by:

verify in interface Parameter

Parameters:

container - the container from which dependencies are resolved.

adapter - the ComponentAdapter that is asking for the verification

expectedType - the required type

expectedNameBinding - Expected parameter name

See Also:

Parameter.verify(org.picocontainer.PicoContainer, org.picocontainer.ComponentAdapter, java.lang.reflect.Type, org.picocontainer.NameBinding, boolean, java.lang.annotation.Annotation)

isAssignable

protected boolean isAssignable(Type expectedType)

Nulls cannot be assigned to primitives.

Parameters:

expectedType -

Returns: