de.jstacs.utils

Class SubclassFinder

java.lang.Object

de.jstacs.utils.SubclassFinder

public class SubclassFinder
extends Object

Utility-class with static methods to

• find all sub-classes of a certain class (or interface) within the scope of the current class-loader
• find all sub-classes of a certain class (or interface) within the scope of the current class-loader that can be instantiated, i.e. that are neither interfaces nor abstract
• filter a set of classes by inheritance from a super-class
• obtain the class of an InstanceParameterSet that can be used to instantiate a sub-class of InstantiableFromParameterSet.
• obtain a SelectionParameter using all possible ParameterSets (for classes that are a subclass of a specified superclass) as elements

The methods may fail to find a certain sub-class, if

• it was loaded by another ClassLoader than the caller
• it was loaded from a physically other place than the super-class, e.g. another jar-file.

Author:

Jens Keilwagen, Jan Grau

Field Summary

Fields

Modifier and Type	Field and Description
static String	includePath This field can be set to include a path into the search performed in findSubclasses(Class, String) thereby enabling to find self-implemented classes not included in the Jstacs class hierarchy.

Constructor Summary

Constructors

Constructor and Description
SubclassFinder()

Method Summary

Methods

Modifier and Type	Method and Description
static <S,T> LinkedList<Class<? extends S>>	filterBySuperclass(Class<S> superclass, LinkedList<Class<? extends T>> listToFilter) Returns a LinkedList of the Class objects for all classes in listToFilter that are sub-classes of superClass.
static <T> LinkedList<Class<? extends T>>	findInstantiableSubclasses(Class<T> clazz, String startPackage) Returns all sub-classes of T that can be instantiated, i.e.
static <T> LinkedList<Class<? extends T>>	findSubclasses(Class<T> clazz, String startPackage) Returns all sub-classes of T including interfaces and abstract classes that are located in a package below startPackage.
static <T> LinkedList<InstanceParameterSet<? extends T>>	getInstanceParameterSets(Class<T> clazz, String startPackage) This method returns a list of InstanceParameterSets that can be used to create a subclass of clazz.
static LinkedList<Class<? extends InstanceParameterSet>>	getParameterSetFor(Class<? extends InstantiableFromParameterSet> clazz) Returns a LinkedList of the classes of the InstanceParameterSets that can be used to instantiate the sub-class of InstantiableFromParameterSet that is given by clazz
static <T> SelectionParameter	getSelectionParameter(Class<? extends ParameterSet> clazz, String startPackage, String name, String comment, boolean required) This method creates an SelectionParameter that contains InstanceParameterSet for each possible class.

Methods inherited from class java.lang.Object

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

Field Detail

includePath

public static String includePath

This field can be set to include a path into the search performed in findSubclasses(Class, String) thereby enabling to find self-implemented classes not included in the Jstacs class hierarchy. The default value of this field is null.

Please use this field very careful, i.e., after setting a specific value and calling findSubclasses(Class, String) it is highly recommended to reset the value. If this is not done, preceeding searches might take longer.

Constructor Detail

SubclassFinder

public SubclassFinder()

Method Detail

findInstantiableSubclasses

public static <T> LinkedList<Class<? extends T>> findInstantiableSubclasses(Class<T> clazz,
                                                            String startPackage)
                                                                 throws ClassNotFoundException,
                                                                        IOException

Returns all sub-classes of T that can be instantiated, i.e. are neither an interface nor abstract, and that are located in a package below startPackage.

Type Parameters:

T - The class to obtain the sub-classes for

Parameters:

clazz - the Class object for T

startPackage - the package under which to search

Returns:

the Class objects for the sub-classes

Throws:

ClassNotFoundException - if one of the classes is present in the file system or jar but cannot be loaded by the class loader

IOException - is thrown if the classes are searched for in a jar file, but that file could not be accessed or read

filterBySuperclass

public static <S,T> LinkedList<Class<? extends S>> filterBySuperclass(Class<S> superclass,
                                                      LinkedList<Class<? extends T>> listToFilter)

Returns a LinkedList of the Class objects for all classes in listToFilter that are sub-classes of superClass.

Type Parameters:

S - the class that is used as filter

T - a common super-class of all classes in listToFilter

Parameters:

superclass - the additional class to use as a filter criterion

listToFilter - the list of classes

Returns:

the filtered list

getParameterSetFor

public static LinkedList<Class<? extends InstanceParameterSet>> getParameterSetFor(Class<? extends InstantiableFromParameterSet> clazz)

Returns a LinkedList of the classes of the InstanceParameterSets that can be used to instantiate the sub-class of InstantiableFromParameterSet that is given by clazz

Parameters:

clazz - the Class object of the sub-class of InstantiableFromParameterSet

Returns:

a LinkedList of Classes of the corresponding InstanceParameterSets

findSubclasses

public static <T> LinkedList<Class<? extends T>> findSubclasses(Class<T> clazz,
                                                String startPackage)
                                                     throws ClassNotFoundException,
                                                            IOException

Returns all sub-classes of T including interfaces and abstract classes that are located in a package below startPackage.

Type Parameters:

T - The class to obtain the sub-classes for

Parameters:

clazz - the Class object for T

startPackage - the package under which to search

Returns:

the Class objects for the sub-classes

Throws:

ClassNotFoundException - if one of the classes is present in the file system or jar but cannot be loaded by the class loader

IOException - is thrown if the classes are searched for in a jar file, but that file could not be accessed or read

getSelectionParameter

public static <T> SelectionParameter getSelectionParameter(Class<? extends ParameterSet> clazz,
                                           String startPackage,
                                           String name,
                                           String comment,
                                           boolean required)
                                                throws Exception

This method creates an SelectionParameter that contains InstanceParameterSet for each possible class. The classes are specified by findInstantiableSubclasses(Class, String) and filterBySuperclass(Class, LinkedList).

Type Parameters:

T - The class to use the sub-classes in the SelectionParameter

Parameters:

clazz - the Class object for T

startPackage - the package under which to start the search

name - the name of the SelectionParameter

comment - the comment for the SelectionParameter

required - whether the SelectionParameter is required

Returns:

a SelectionParameter that contains InstanceParameterSet for each possible class.

Throws:

Exception - if the SelectionParameter could not be created properly

See Also:

findInstantiableSubclasses(Class, String), filterBySuperclass(Class, LinkedList), getInstanceParameterSets(Class, String)

getInstanceParameterSets

public static <T> LinkedList<InstanceParameterSet<? extends T>> getInstanceParameterSets(Class<T> clazz,
                                                                         String startPackage)
                                                                              throws ClassNotFoundException,
                                                                                     IOException,
                                                                                     InstantiationException,
                                                                                     IllegalAccessException

This method returns a list of InstanceParameterSets that can be used to create a subclass of clazz. The classes are specified by findInstantiableSubclasses(Class, String) and filterBySuperclass(Class, LinkedList).

Type Parameters:

T - The class to use the sub-classes in the SelectionParameter

Parameters:

clazz - the Class object for T

startPackage - the package under which to start the search

Returns:

a LinkedList that contains InstanceParameterSet for each possible class.

Throws:

InstantiationException - if any InstanceParameterSet has no nullary constructor; or if the instantiation fails for some other reason

IllegalAccessException - if any InstanceParameterSet or its nullary constructor is not accessible

ClassNotFoundException - if one of the classes is present in the file system or jar but cannot be loaded by the class loader

IOException - if the classes are searched for in a jar file, but that file could not be accessed or read

See Also:

findInstantiableSubclasses(Class, String), filterBySuperclass(Class, LinkedList)