com.google.common.reflect
Class TypeToken<T>

java.lang.Object
  com.google.common.reflect.TypeToken<T>

All Implemented Interfaces:

Serializable

@Beta
public abstract class TypeToken<T>
extends Object
implements Serializable

A Type with generics.

Operations that are otherwise only available in Class are implemented to support Type, for instance isAssignableFrom(com.google.common.reflect.TypeToken), isArray() and getGenericInterfaces() 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 the listType() 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, but with one important difference: it supports non-reified types such as T, List<T> or even List<? extends Number>; while TypeLiteral does not. TypeToken is also serializable and offers numerous additional utility methods.

Since:

12.0

Author:

Bob Lee, Sven Mawson, Ben Yu

See Also:

Serialized Form

Nested Class Summary

class

TypeToken.TypeSet The set of interfaces and classes that T is or is a subtype of.

Constructor Summary

protected	TypeToken() Constructs a new type token of T.
protected	TypeToken(Class<?> declaringClass) Constructs a new type token of T while resolving free type variables in the context of declaringClass.

Method Summary

boolean	equals(Object o) Returns true if o is another TypeToken that represents the same Type.
TypeToken<?>	getComponentType() Returns the array component type if this type represents an array (int[], T[], <? extends Map<String, Integer>[]> etc.), or else null is returned.
Class<? super T>	getRawType() Returns the raw type of T.
TypeToken<? extends T>	getSubtype(Class<?> subclass) Returns subtype of this with subclass as the raw class.
TypeToken<? super T>	getSupertype(Class<? super T> superclass) Returns the generic form of superclass.
Type	getType() Returns the represented type.
TypeToken.TypeSet	getTypes() Returns the set of interfaces and classes that this type is or is a subtype of.
int	hashCode()
boolean	isArray() Returns true if this type is known to be an array type, such as int[], T[], <? extends Map<String, Integer>[]> etc.
boolean	isAssignableFrom(Type type) Check if this type is assignable from the given type.
boolean	isAssignableFrom(TypeToken<?> type) Returns true if this type is assignable from the given type.
static <T> TypeToken<T>	of(Class<T> type) Returns an instance of type token that wraps type.
static TypeToken<?>	of(Type type) Returns an instance of type token that wraps type.
TypeToken<?>	resolveType(Type type) Resolves the given type against the type context represented by this type.
String	toString()
<X> TypeToken<T>	where(TypeParameter<X> typeParam, Class<X> typeArg) Returns a new TypeToken where type variables represented by typeParam are substituted by typeArg.
<X> TypeToken<T>	where(TypeParameter<X> typeParam, TypeToken<X> typeArg) Returns a new TypeToken where type variables represented by typeParam are substituted by typeArg.
protected Object	writeReplace() Implemented to support serialization of subclasses.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

TypeToken

protected TypeToken()

Constructs a new type token of T.

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

protected TypeToken(Class<?> declaringClass)

Constructs a new type token of T while resolving free type variables in the context of declaringClass.

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 Detail

of

public static <T> TypeToken<T> of(Class<T> type)

Returns an instance of type token that wraps type.

of

public static TypeToken<?> of(Type type)

Returns an instance of type token that wraps type.

getRawType

public final Class<? super T> getRawType()

Returns the raw type of T. Formally speaking, if T is returned by Method.getGenericReturnType(), the raw type is what's returned by Method.getReturnType() of the same method object. Specifically:

• If T is a Class itself, T itself is returned.
• If T is a ParameterizedType, the raw type of the parameterized type is returned.
• If T is a GenericArrayType, 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.

getType

public final Type getType()

Returns the represented type.

where

public final <X> TypeToken<T> where(TypeParameter<X> typeParam,
                                    TypeToken<X> typeArg)

Returns a new TypeToken where type variables represented by typeParam are substituted by typeArg. For example, it can be used to construct Map<K, V> for any K and V 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 variable

typeArg - the actual type to substitute

where

public final <X> TypeToken<T> where(TypeParameter<X> typeParam,
                                    Class<X> typeArg)

Returns a new TypeToken where type variables represented by typeParam are substituted by typeArg. For example, it can be used to construct Map<K, V> for any K and V 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 variable

typeArg - the actual type to substitute

resolveType

public final TypeToken<?> resolveType(Type type)

Resolves the given type 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

public final TypeToken.TypeSet 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

public final TypeToken<? super T> getSupertype(Class<? super T> superclass)

Returns the generic form of superclass. For example, if this is ArrayList<String>, Iterable<String> is returned given the input Iterable.class.

getSubtype

public final TypeToken<? extends T> getSubtype(Class<?> subclass)

Returns subtype of this with subclass as the raw class. For example, if this is Iterable<String> and subclass is List, List<String> is returned.

isAssignableFrom

public final boolean isAssignableFrom(TypeToken<?> type)

Returns true if this type is assignable from the given type.

isAssignableFrom

public final boolean isAssignableFrom(Type type)

Check if this type is assignable from the given type.

isArray

public final boolean isArray()

Returns true if this type is known to be an array type, such as int[], T[], <? extends Map<String, Integer>[]> etc.

getComponentType

@Nullable
public final TypeToken<?> getComponentType()

Returns the array component type if this type represents an array (int[], T[], <? extends Map<String, Integer>[]> etc.), or else null is returned.

equals

public boolean equals(@Nullable
                      Object o)

Returns true if o is another TypeToken that represents the same Type.

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object

writeReplace

protected Object writeReplace()

Implemented to support serialization of subclasses.