Class TypeToken<T>
- All Implemented Interfaces:
Serializable
Type
with generics.
Operations that are otherwise only available in Class
are implemented to support
Type
, for example isSubtypeOf(com.google.common.reflect.TypeToken<?>)
, isArray()
and getComponentType()
.
It also provides additional utilities such as getTypes()
, resolveType(java.lang.reflect.Type)
, etc.
There are three ways to get a TypeToken
instance:
- Wrap a
Type
obtained via reflection. For example:TypeToken.of(method.getGenericReturnType())
. - Capture a generic type with a (usually anonymous) subclass. For example:
new TypeToken<List<String>>() {}
Note that it's critical that the actual type argument is carried by a subclass. The following code is wrong because it only captures the
<T>
type variable of thelistType()
method signature; while<String>
is lost in erasure:class Util { static <T> TypeToken<List<T>> listType() { return new TypeToken<List<T>>() {}; } } TypeToken<List<String>> stringListType = Util.<String>listType();
- Capture a generic type with a (usually anonymous) subclass and resolve it against a context
class that knows what the type parameters are. For example:
abstract class IKnowMyType<T> { TypeToken<T> type = new TypeToken<T>(getClass()) {}; } new IKnowMyType<String>() {}.type => String
TypeToken
is serializable when no type variable is contained in the type.
Note to Guice users: TypeToken
is similar to Guice's TypeLiteral
class except
that it is serializable and offers numerous additional utility methods.
- Since:
- 12.0
- Author:
- Bob Lee, Sven Mawson, Ben Yu
- See Also:
-
Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionclass
The set of interfaces and classes thatT
is or is a subtype of. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionconstructor
(Constructor<?> constructor) boolean
Returns the array component type if this type represents an array (int[]
,T[]
,<? extends Map<String, Integer>[]>
etc.), or elsenull
is returned.Returns the raw type ofT
.getSubtype
(Class<?> subclass) Returns subtype ofthis
withsubclass
as the raw class.getSupertype
(Class<? super T> superclass) Returns the generic form ofsuperclass
.final Type
getType()
Returns the represented type.getTypes()
Returns the set of interfaces and classes that this type is or is a subtype of.int
hashCode()
final boolean
isArray()
Returns true if this type is known to be an array type, such asint[]
,T[]
,<? extends Map<String, Integer>[]>
etc.final boolean
Returns true if this type is one of the nine primitive types (includingvoid
).final boolean
isSubtypeOf
(TypeToken<?> type) Returns true if this type is a subtype of the giventype
.final boolean
isSubtypeOf
(Type supertype) Returns true if this type is a subtype of the giventype
.final boolean
isSupertypeOf
(TypeToken<?> type) Returns true if this type is a supertype of the giventype
.final boolean
isSupertypeOf
(Type type) Returns true if this type is a supertype of the giventype
.static <T> TypeToken
<T> Returns an instance of type token that wrapstype
.static TypeToken
<?> Returns an instance of type token that wrapstype
.final TypeToken
<?> resolveType
(Type type) Resolves the giventype
against the type context represented by this type.toString()
unwrap()
Returns the corresponding primitive type if this is a wrapper type; otherwise returnsthis
itself.where
(TypeParameter<X> typeParam, TypeToken<X> typeArg) Returns a newTypeToken
where type variables represented bytypeParam
are substituted bytypeArg
.where
(TypeParameter<X> typeParam, Class<X> typeArg) Returns a newTypeToken
where type variables represented bytypeParam
are substituted bytypeArg
.wrap()
Returns the corresponding wrapper type if this is a primitive type; otherwise returnsthis
itself.protected Object
Implemented to support serialization of subclasses.
-
Constructor Details
-
TypeToken
protected TypeToken()Constructs a new type token ofT
.Clients create an empty anonymous subclass. Doing so embeds the type parameter in the anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
For example:
TypeToken<List<String>> t = new TypeToken<List<String>>() {};
-
TypeToken
Constructs a new type token ofT
while resolving free type variables in the context ofdeclaringClass
.Clients create an empty anonymous subclass. Doing so embeds the type parameter in the anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.
For example:
abstract class IKnowMyType<T> { TypeToken<T> getMyType() { return new TypeToken<T>(getClass()) {}; } } new IKnowMyType<String>() {}.getMyType() => String
-
-
Method Details
-
of
-
of
-
getRawType
Returns the raw type ofT
. Formally speaking, ifT
is returned byMethod.getGenericReturnType()
, the raw type is what's returned byMethod.getReturnType()
of the same method object. Specifically:- If
T
is aClass
itself,T
itself is returned. - If
T
is aParameterizedType
, the raw type of the parameterized type is returned. - If
T
is aGenericArrayType
, the returned type is the corresponding array class. For example:List<Integer>[] => List[]
. - If
T
is a type variable or a wildcard type, the raw type of the first upper bound is returned. For example:<X extends Foo> => Foo
.
- If
-
getType
-
where
Returns a newTypeToken
where type variables represented bytypeParam
are substituted bytypeArg
. For example, it can be used to constructMap<K, V>
for anyK
andV
type:static <K, V> TypeToken<Map<K, V>> mapOf( TypeToken<K> keyType, TypeToken<V> valueType) { return new TypeToken<Map<K, V>>() {} .where(new TypeParameter<K>() {}, keyType) .where(new TypeParameter<V>() {}, valueType); }
- Type Parameters:
X
- The parameter type- Parameters:
typeParam
- the parameter type variabletypeArg
- the actual type to substitute
-
where
Returns a newTypeToken
where type variables represented bytypeParam
are substituted bytypeArg
. For example, it can be used to constructMap<K, V>
for anyK
andV
type:static <K, V> TypeToken<Map<K, V>> mapOf( Class<K> keyType, Class<V> valueType) { return new TypeToken<Map<K, V>>() {} .where(new TypeParameter<K>() {}, keyType) .where(new TypeParameter<V>() {}, valueType); }
- Type Parameters:
X
- The parameter type- Parameters:
typeParam
- the parameter type variabletypeArg
- the actual type to substitute
-
resolveType
Resolves the giventype
against the type context represented by this type. For example:new TypeToken<List<String>>() {}.resolveType( List.class.getMethod("get", int.class).getGenericReturnType()) => String.class
-
getTypes
Returns the set of interfaces and classes that this type is or is a subtype of. The returned types are parameterized with proper type arguments.Subtypes are always listed before supertypes. But the reverse is not true. A type isn't necessarily a subtype of all the types following. Order between types without subtype relationship is arbitrary and not guaranteed.
If this type is a type variable or wildcard, upper bounds that are themselves type variables aren't included (their super interfaces and superclasses are).
-
getSupertype
Returns the generic form ofsuperclass
. For example, if this isArrayList<String>
,Iterable<String>
is returned given the inputIterable.class
. -
getSubtype
Returns subtype ofthis
withsubclass
as the raw class. For example, if this isIterable<String>
andsubclass
isList
,List<String>
is returned. -
isSupertypeOf
Returns true if this type is a supertype of the giventype
. "Supertype" is defined according to the rules for type arguments introduced with Java generics.- Since:
- 19.0
-
isSupertypeOf
Returns true if this type is a supertype of the giventype
. "Supertype" is defined according to the rules for type arguments introduced with Java generics.- Since:
- 19.0
-
isSubtypeOf
Returns true if this type is a subtype of the giventype
. "Subtype" is defined according to the rules for type arguments introduced with Java generics.- Since:
- 19.0
-
isSubtypeOf
Returns true if this type is a subtype of the giventype
. "Subtype" is defined according to the rules for type arguments introduced with Java generics.- Since:
- 19.0
-
isArray
Returns true if this type is known to be an array type, such asint[]
,T[]
,<? extends Map<String, Integer>[]>
etc. -
isPrimitive
Returns true if this type is one of the nine primitive types (includingvoid
).- Since:
- 15.0
-
wrap
-
unwrap
-
getComponentType
Returns the array component type if this type represents an array (int[]
,T[]
,<? extends Map<String, Integer>[]>
etc.), or elsenull
is returned. -
method
-
constructor
- Since:
- 14.0
-
equals
-
hashCode
-
toString
-
writeReplace
Implemented to support serialization of subclasses.
-