Package 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

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	TypeUtils.WildcardTypeBuilder	WildcardType builder.

Field Summary

Fields

Modifier and Type	Field	Description
static WildcardType	WILDCARD_ALL	A wildcard instance matching ?.

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method	Description
static boolean	containsTypeVariables(Type type)	Learn, recursively, whether any of the type parameters associated with type are bound to variables.
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 boolean	equals(Type t1, Type t2)	Check equality of types.
static GenericArrayType	genericArrayType(Type componentType)	Create a generic array type instance.
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<K,V>.Inner<T>.DeepInner<E> .
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 ParameterizedType	parameterize(Class<?> raw, Type... typeArguments)	Create a parameterized type instance.
static ParameterizedType	parameterize(Class<?> raw, Map<TypeVariable<?>,Type> typeArgMappings)	Create a parameterized type instance.
static ParameterizedType	parameterizeWithOwner(Type owner, Class<?> raw, Type... typeArguments)	Create a parameterized type instance.
static ParameterizedType	parameterizeWithOwner(Type owner, Class<?> raw, Map<TypeVariable<?>,Type> typeArgMappings)	Create a parameterized type instance.
static String	toLongString(TypeVariable<?> var)	Format a TypeVariable including its GenericDeclaration.
static String	toString(Type type)	Present a given type as a Java-esque String.
static boolean	typesSatisfyVariables(Map<TypeVariable<?>,Type> typeVarAssigns)	Determines whether or not specified types satisfy the bounds of their mapped type variables.
static Type	unrollVariables(Map<TypeVariable<?>,Type> typeArguments, Type type)	Get a type representing type with variable assignments "unrolled."
static TypeUtils.WildcardTypeBuilder	wildcardType()	Get a TypeUtils.WildcardTypeBuilder.
static <T> Typed<T>	wrap(Class<T> type)	Wrap the specified Class in a Typed wrapper.
static <T> Typed<T>	wrap(Type type)	Wrap the specified Type in a Typed wrapper.

Methods inherited from class java.lang.Object

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

Field Detail

WILDCARD_ALL

public static final WildcardType WILDCARD_ALL

A wildcard instance matching ?.

Since:

3.2

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<K,V>.Inner<T>.DeepInner<E> . 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<? extends Map<Integer, ? extends Collection<?>>>, the parameter of TreeSet is ? extends Map<Integer, ? extends Collection<?>>.

Parameters:

cls - the class whose type parameters are to be determined, not null

superType - the super type from which cls's type arguments are to be determined, not null

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 if 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, not null.

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, not null

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, not null

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, not null

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 <T, S extends T>), uses another as a type parameter (such as <T, S extends Comparable>>), 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, not null.

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

unrollVariables

public static Type unrollVariables(Map<TypeVariable<?>,Type> typeArguments,
                                   Type type)

Get a type representing type with variable assignments "unrolled."

Parameters:

typeArguments - as from getTypeArguments(Type, Class)

type - the type to unroll variable assignments for

Returns:

Type

Since:

3.2

containsTypeVariables

public static boolean containsTypeVariables(Type type)

Learn, recursively, whether any of the type parameters associated with type are bound to variables.

Parameters:

type - the type to check for type variables

Returns:

boolean

Since:

3.2

parameterize

public static final ParameterizedType parameterize(Class<?> raw,
                                                   Type... typeArguments)

Create a parameterized type instance.

Parameters:

raw - the raw class to create a parameterized type instance for

typeArguments - the types used for parameterization

Returns:

ParameterizedType

Since:

3.2

parameterize

public static final ParameterizedType parameterize(Class<?> raw,
                                                   Map<TypeVariable<?>,Type> typeArgMappings)

Create a parameterized type instance.

Parameters:

raw - the raw class to create a parameterized type instance for

typeArgMappings - the mapping used for parameterization

Returns:

ParameterizedType

Since:

3.2

parameterizeWithOwner

public static final ParameterizedType parameterizeWithOwner(Type owner,
                                                            Class<?> raw,
                                                            Type... typeArguments)

Create a parameterized type instance.

Parameters:

owner - the owning type

raw - the raw class to create a parameterized type instance for

typeArguments - the types used for parameterization

Returns:

ParameterizedType

Since:

3.2

parameterizeWithOwner

public static final ParameterizedType parameterizeWithOwner(Type owner,
                                                            Class<?> raw,
                                                            Map<TypeVariable<?>,Type> typeArgMappings)

Create a parameterized type instance.

Parameters:

owner - the owning type

raw - the raw class to create a parameterized type instance for

typeArgMappings - the mapping used for parameterization

Returns:

ParameterizedType

Since:

3.2

wildcardType

public static TypeUtils.WildcardTypeBuilder wildcardType()

Get a TypeUtils.WildcardTypeBuilder.

Returns:

TypeUtils.WildcardTypeBuilder

Since:

3.2

genericArrayType

public static GenericArrayType genericArrayType(Type componentType)

Create a generic array type instance.

Parameters:

componentType - the type of the elements of the array. For example the component type of boolean[] is boolean

Returns:

GenericArrayType

Since:

3.2

equals

public static boolean equals(Type t1,
                             Type t2)

Check equality of types.

Parameters:

t1 - the first type

t2 - the second type

Returns:

boolean

Since:

3.2

toString

public static String toString(Type type)

Present a given type as a Java-esque String.

Parameters:

type - the type to create a String representation for, not null

Returns:

String

Since:

3.2

toLongString

public static String toLongString(TypeVariable<?> var)

Format a TypeVariable including its GenericDeclaration.

Parameters:

var - the type variable to create a String representation for, not null

Returns:

String

Since:

3.2

wrap

public static <T> Typed<T> wrap(Type type)

Wrap the specified Type in a Typed wrapper.

Type Parameters:

T - inferred generic type

Parameters:

type - to wrap

Returns:

Typed<T>

Since:

3.2

wrap

public static <T> Typed<T> wrap(Class<T> type)

Wrap the specified Class in a Typed wrapper.

Type Parameters:

T - generic type

Parameters:

type - to wrap

Returns:

Typed<T>

Since:

3.2