org.apache.commons.lang3.reflect
Class TypeUtils

java.lang.Object
  org.apache.commons.lang3.reflect.TypeUtils

public class TypeUtils
extends Object

Utility methods focusing on type inspection, particularly with regard to generics.

Since:

3.0

Version:

$Id: TypeUtils.java 1144929 2011-07-10 18:26:16Z ggregory $

Constructor Summary

TypeUtils()
TypeUtils instances should NOT be constructed in standard programming.

Method Summary

static Map<TypeVariable<?>,Type>	determineTypeArguments(Class<?> cls, ParameterizedType superType) Tries to determine the type arguments of a class/interface based on a super parameterized type's type arguments.
static Type	getArrayComponentType(Type type) Get the array component type of type.
static Type[]	getImplicitBounds(TypeVariable<?> typeVariable) Returns an array containing the sole type of Object if TypeVariable.getBounds() returns an empty array.
static Type[]	getImplicitLowerBounds(WildcardType wildcardType) Returns an array containing a single value of null if WildcardType.getLowerBounds() returns an empty array.
static Type[]	getImplicitUpperBounds(WildcardType wildcardType) Returns an array containing the sole value of Object if WildcardType.getUpperBounds() returns an empty array.
static Class<?>	getRawType(Type type, Type assigningType) Get the raw type of a Java type, given its context.
static Map<TypeVariable<?>,Type>	getTypeArguments(ParameterizedType type) Retrieves all the type arguments for this parameterized type including owner hierarchy arguments such as Outer.Inner.DeepInner .
static Map<TypeVariable<?>,Type>	getTypeArguments(Type type, Class<?> toClass) Gets the type arguments of a class/interface based on a subtype.
static boolean	isArrayType(Type type) Learn whether the specified type denotes an array type.
static boolean	isAssignable(Type type, Type toType) Checks if the subject type may be implicitly cast to the target type following the Java generics rules.
static boolean	isInstance(Object value, Type type) Checks if the given value can be assigned to the target type following the Java generics rules.
static Type[]	normalizeUpperBounds(Type[] bounds) This method strips out the redundant upper bound types in type variable types and wildcard types (or it would with wildcard types if multiple upper bounds were allowed).
static boolean	typesSatisfyVariables(Map<TypeVariable<?>,Type> typeVarAssigns) Determines whether or not specified types satisfy the bounds of their mapped type variables.

Methods inherited from class java.lang.Object

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

Constructor Detail

TypeUtils

public TypeUtils()

TypeUtils instances should NOT be constructed in standard programming. Instead, the class should be used as TypeUtils.isAssignable(cls, toClass).

This constructor is public to permit tools that require a JavaBean instance to operate.

Method Detail

isAssignable

public static boolean isAssignable(Type type,
                                   Type toType)

Checks if the subject type may be implicitly cast to the target type following the Java generics rules. If both types are Class objects, the method returns the result of ClassUtils.isAssignable(Class, Class).

Parameters:

type - the subject type to be assigned to the target type

toType - the target type

Returns:

true if type is assignable to toType.

getTypeArguments

public static Map<TypeVariable<?>,Type> getTypeArguments(ParameterizedType type)

Retrieves all the type arguments for this parameterized type including owner hierarchy arguments such as Outer.Inner.DeepInner . The arguments are returned in a Map specifying the argument type for each TypeVariable.

Parameters:

type - specifies the subject parameterized type from which to harvest the parameters.

Returns:

a map of the type arguments to their respective type variables.

getTypeArguments

public static Map<TypeVariable<?>,Type> getTypeArguments(Type type,
                                                         Class<?> toClass)

Gets the type arguments of a class/interface based on a subtype. For instance, this method will determine that both of the parameters for the interface Map are Object for the subtype Properties even though the subtype does not directly implement the Map interface.

This method returns null if type is not assignable to toClass. It returns an empty map if none of the classes or interfaces in its inheritance hierarchy specify any type arguments.

A side-effect of this method is that it also retrieves the type arguments for the classes and interfaces that are part of the hierarchy between type and toClass. So with the above example, this method will also determine that the type arguments for Hashtable are also both Object. In cases where the interface specified by toClass is (indirectly) implemented more than once (e.g. where toClass specifies the interface Iterable and type specifies a parameterized type that implements both Set and Collection), this method will look at the inheritance hierarchy of only one of the implementations/subclasses; the first interface encountered that isn't a subinterface to one of the others in the type to toClass hierarchy.

Parameters:

type - the type from which to determine the type parameters of toClass

toClass - the class whose type parameters are to be determined based on the subtype type

Returns:

a map of the type assignments for the type variables in each type in the inheritance hierarchy from type to toClass inclusive.

determineTypeArguments

public static Map<TypeVariable<?>,Type> determineTypeArguments(Class<?> cls,
                                                               ParameterizedType superType)

Tries to determine the type arguments of a class/interface based on a super parameterized type's type arguments. This method is the inverse of getTypeArguments(Type, Class) which gets a class/interface's type arguments based on a subtype. It is far more limited in determining the type arguments for the subject class's type variables in that it can only determine those parameters that map from the subject Class object to the supertype.

Example: TreeSet sets its parameter as the parameter for NavigableSet, which in turn sets the parameter of SortedSet, which in turn sets the parameter of Set, which in turn sets the parameter of Collection, which in turn sets the parameter of Iterable. Since TreeSet's parameter maps (indirectly) to Iterable's parameter, it will be able to determine that based on the super type Iterable>>, the parameter of TreeSet is ? extends Map>.

Parameters:

cls - the class whose type parameters are to be determined

superType - the super type from which cls's type arguments are to be determined

Returns:

a map of the type assignments that could be determined for the type variables in each type in the inheritance hierarchy from type to toClass inclusive.

isInstance

public static boolean isInstance(Object value,
                                 Type type)

Checks if the given value can be assigned to the target type following the Java generics rules.

Parameters:

value - the value to be checked

type - the target type

Returns:

true of value is an instance of type.

normalizeUpperBounds

public static Type[] normalizeUpperBounds(Type[] bounds)

This method strips out the redundant upper bound types in type variable types and wildcard types (or it would with wildcard types if multiple upper bounds were allowed).

Example: with the variable type declaration:

 <K extends java.util.Collection<String> &
 java.util.List<String>> 

since List is a subinterface of Collection, this method will return the bounds as if the declaration had been:

 <K extends java.util.List<String>> 

Parameters:

bounds - an array of types representing the upper bounds of either WildcardType or TypeVariable.

Returns:

an array containing the values from bounds minus the redundant types.

getImplicitBounds

public static Type[] getImplicitBounds(TypeVariable<?> typeVariable)

Returns an array containing the sole type of Object if TypeVariable.getBounds() returns an empty array. Otherwise, it returns the result of TypeVariable.getBounds() passed into normalizeUpperBounds(java.lang.reflect.Type[]).

Parameters:

typeVariable - the subject type variable

Returns:

a non-empty array containing the bounds of the type variable.

getImplicitUpperBounds

public static Type[] getImplicitUpperBounds(WildcardType wildcardType)

Returns an array containing the sole value of Object if WildcardType.getUpperBounds() returns an empty array. Otherwise, it returns the result of WildcardType.getUpperBounds() passed into normalizeUpperBounds(java.lang.reflect.Type[]).

Parameters:

wildcardType - the subject wildcard type

Returns:

a non-empty array containing the upper bounds of the wildcard type.

getImplicitLowerBounds

public static Type[] getImplicitLowerBounds(WildcardType wildcardType)

Returns an array containing a single value of null if WildcardType.getLowerBounds() returns an empty array. Otherwise, it returns the result of WildcardType.getLowerBounds().

Parameters:

wildcardType - the subject wildcard type

Returns:

a non-empty array containing the lower bounds of the wildcard type.

typesSatisfyVariables

public static boolean typesSatisfyVariables(Map<TypeVariable<?>,Type> typeVarAssigns)

Determines whether or not specified types satisfy the bounds of their mapped type variables. When a type parameter extends another (such as ), uses another as a type parameter (such as ), or otherwise depends on another type variable to be specified, the dependencies must be included in typeVarAssigns.

Parameters:

typeVarAssigns - specifies the potential types to be assigned to the type variables.

Returns:

whether or not the types can be assigned to their respective type variables.

getRawType

public static Class<?> getRawType(Type type,
                                  Type assigningType)

Get the raw type of a Java type, given its context. Primarily for use with TypeVariables and GenericArrayTypes, or when you do not know the runtime type of type: if you know you have a Class instance, it is already raw; if you know you have a ParameterizedType, its raw type is only a method call away.

Parameters:

type - to resolve

assigningType - type to be resolved against

Returns:

the resolved Class object or null if the type could not be resolved

isArrayType

public static boolean isArrayType(Type type)

Learn whether the specified type denotes an array type.

Parameters:

type - the type to be checked

Returns:

true if type is an array class or a GenericArrayType.

getArrayComponentType

public static Type getArrayComponentType(Type type)

Get the array component type of type.

Parameters:

type - the type to be checked

Returns:

component type or null if type is not an array type