Class TypeToken<T>
T
. Java doesn't yet provide a way to represent generic types,
so this class does. Forces clients to create a subclass of this class which enables retrieval the
type information even at runtime.
For example, to create a type literal for List<String>
, you can create an empty
anonymous class:
TypeToken<List<String>> list = new TypeToken<List<String>>() {};
Capturing a type variable as type argument of an anonymous TypeToken
subclass is not
allowed, for example TypeToken<List<T>>
. Due to type erasure the runtime type of a type
variable is not available to Gson and therefore it cannot provide the functionality one might
expect. This would give a false sense of type-safety at compile time and could lead to an
unexpected ClassCastException
at runtime.
If the type arguments of the parameterized type are only available at runtime, for example
when you want to create a List<E>
based on a Class<E>
representing the element
type, the method getParameterized(Type, Type...)
can be used.
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Field Summary
Fields -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprivate static IllegalArgumentException
buildUnsupportedTypeException
(Type token, Class<?>... expected) final boolean
static <T> TypeToken
<T> Gets type literal for the givenClass
instance.static TypeToken
<?> Gets type literal for the givenType
instance.static TypeToken
<?> Gets type literal for the array type whose elements are all instances ofcomponentType
.static TypeToken
<?> getParameterized
(Type rawType, Type... typeArguments) Gets a type literal for the parameterized type represented by applyingtypeArguments
torawType
.Returns the raw (non-generic) type for this type.final Type
getType()
Gets underlyingType
instance.private Type
Verifies thatthis
is an instance of a direct subclass of TypeToken and returns the type argument forT
incanonical form
.final int
hashCode()
boolean
isAssignableFrom
(TypeToken<?> token) Deprecated.this implementation may be inconsistent with javac for types with wildcards.boolean
isAssignableFrom
(Class<?> cls) Deprecated.this implementation may be inconsistent with javac for types with wildcards.boolean
isAssignableFrom
(Type from) Deprecated.this implementation may be inconsistent with javac for types with wildcards.private static boolean
isAssignableFrom
(Type from, GenericArrayType to) Private helper function that performs some assignability checks for the provided GenericArrayType.private static boolean
isAssignableFrom
(Type from, ParameterizedType to, Map<String, Type> typeVarMap) Private recursive helper function to actually do the type-safe checking of assignability.private static boolean
private static boolean
Checks if two types are the same or are equivalent under a variable mapping given in the type map that was provided.final String
toString()
private static boolean
typeEquals
(ParameterizedType from, ParameterizedType to, Map<String, Type> typeVarMap) Checks if two parameterized types are exactly equal, under the variable replacement described in the typeVarMap.private static void
verifyNoTypeVariable
(Type type)
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Field Details
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rawType
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type
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hashCode
private final int hashCode
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Constructor Details
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TypeToken
protected TypeToken()Constructs a new type literal. Derives represented class from type parameter.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:
new TypeToken<List<String>>() {}
- Throws:
IllegalArgumentException
- If the anonymousTypeToken
subclass captures a type variable, for exampleTypeToken<List<T>>
. See theTypeToken
class documentation for more details.
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TypeToken
Unsafe. Constructs a type literal manually.
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Method Details
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isCapturingTypeVariablesForbidden
private static boolean isCapturingTypeVariablesForbidden() -
getTypeTokenTypeArgument
Verifies thatthis
is an instance of a direct subclass of TypeToken and returns the type argument forT
incanonical form
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verifyNoTypeVariable
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getRawType
Returns the raw (non-generic) type for this type. -
getType
Gets underlyingType
instance. -
isAssignableFrom
Deprecated.this implementation may be inconsistent with javac for types with wildcards.Check if this type is assignable from the given class object. -
isAssignableFrom
Deprecated.this implementation may be inconsistent with javac for types with wildcards.Check if this type is assignable from the given Type. -
isAssignableFrom
Deprecated.this implementation may be inconsistent with javac for types with wildcards.Check if this type is assignable from the given type token. -
isAssignableFrom
Private helper function that performs some assignability checks for the provided GenericArrayType. -
isAssignableFrom
private static boolean isAssignableFrom(Type from, ParameterizedType to, Map<String, Type> typeVarMap) Private recursive helper function to actually do the type-safe checking of assignability. -
typeEquals
private static boolean typeEquals(ParameterizedType from, ParameterizedType to, Map<String, Type> typeVarMap) Checks if two parameterized types are exactly equal, under the variable replacement described in the typeVarMap. -
buildUnsupportedTypeException
private static IllegalArgumentException buildUnsupportedTypeException(Type token, Class<?>... expected) -
matches
Checks if two types are the same or are equivalent under a variable mapping given in the type map that was provided. -
hashCode
public final int hashCode() -
equals
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toString
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get
Gets type literal for the givenType
instance. -
get
Gets type literal for the givenClass
instance. -
getParameterized
Gets a type literal for the parameterized type represented by applyingtypeArguments
torawType
. This is mainly intended for situations where the type arguments are not available at compile time. The following example shows how a type token forMap<K, V>
can be created:
As seen here the result is aClass<K> keyClass = ...; Class<V> valueClass = ...; TypeToken<?> mapTypeToken = TypeToken.getParameterized(Map.class, keyClass, valueClass);
TypeToken<?>
; this method cannot provide any type-safety, and care must be taken to pass in the correct number of type arguments.If
rawType
is a non-generic class and no type arguments are provided, this method simply delegates toget(Class)
and creates aTypeToken(Class)
.- Throws:
IllegalArgumentException
- IfrawType
is not of typeClass
, or if the type arguments are invalid for the raw type
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getArray
Gets type literal for the array type whose elements are all instances ofcomponentType
.
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