Package com.google.gson.reflect

Class TypeToken<T>

  • public class TypeToken<T>
extends java.lang.Object
    Represents a generic type 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.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private int hashCode  
      private java.lang.Class<? super T> rawType  
      private java.lang.reflect.Type type  

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      protected TypeToken()
      Constructs a new type literal.
      private TypeToken​(java.lang.reflect.Type type)
      Unsafe.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods 
      Modifier and Type Method Description
      private static java.lang.IllegalArgumentException buildUnsupportedTypeException​(java.lang.reflect.Type token, java.lang.Class<?>... expected)  
      boolean equals​(java.lang.Object o)  
      static <T> TypeToken<T> get​(java.lang.Class<T> type)
      Gets type literal for the given Class instance.
      static TypeToken<?> get​(java.lang.reflect.Type type)
      Gets type literal for the given Type instance.
      static TypeToken<?> getArray​(java.lang.reflect.Type componentType)
      Gets type literal for the array type whose elements are all instances of componentType.
      static TypeToken<?> getParameterized​(java.lang.reflect.Type rawType, java.lang.reflect.Type... typeArguments)
      Gets a type literal for the parameterized type represented by applying typeArguments to rawType.
      java.lang.Class<? super T> getRawType()
      Returns the raw (non-generic) type for this type.
      java.lang.reflect.Type getType()
      Gets underlying Type instance.
      private java.lang.reflect.Type getTypeTokenTypeArgument()
      Verifies that this is an instance of a direct subclass of TypeToken and returns the type argument for T in canonical form.
      int hashCode()  
      boolean isAssignableFrom​(TypeToken<?> token)
      Deprecated.
      this implementation may be inconsistent with javac for types with wildcards.
      boolean isAssignableFrom​(java.lang.Class<?> cls)
      Deprecated.
      this implementation may be inconsistent with javac for types with wildcards.
      boolean isAssignableFrom​(java.lang.reflect.Type from)
      Deprecated.
      this implementation may be inconsistent with javac for types with wildcards.
      private static boolean isAssignableFrom​(java.lang.reflect.Type from, java.lang.reflect.GenericArrayType to)
      Private helper function that performs some assignability checks for the provided GenericArrayType.
      private static boolean isAssignableFrom​(java.lang.reflect.Type from, java.lang.reflect.ParameterizedType to, java.util.Map<java.lang.String,​java.lang.reflect.Type> typeVarMap)
      Private recursive helper function to actually do the type-safe checking of assignability.
      private static boolean isCapturingTypeVariablesForbidden()  
      private static boolean matches​(java.lang.reflect.Type from, java.lang.reflect.Type to, java.util.Map<java.lang.String,​java.lang.reflect.Type> typeMap)
      Checks if two types are the same or are equivalent under a variable mapping given in the type map that was provided.
      java.lang.String toString()  
      private static boolean typeEquals​(java.lang.reflect.ParameterizedType from, java.lang.reflect.ParameterizedType to, java.util.Map<java.lang.String,​java.lang.reflect.Type> typeVarMap)
      Checks if two parameterized types are exactly equal, under the variable replacement described in the typeVarMap.
      private static void verifyNoTypeVariable​(java.lang.reflect.Type type)  

      • Methods inherited from class java.lang.Object

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

    • Field Detail

      • rawType

        private final java.lang.Class<? super T> rawType

      • type

        private final java.lang.reflect.Type type

      • hashCode

        private final int hashCode

    • Constructor Detail

      • 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:
        java.lang.IllegalArgumentException - If the anonymous TypeToken subclass captures a type variable, for example TypeToken<List<T>>. See the TypeToken class documentation for more details.

      • TypeToken

        private TypeToken​(java.lang.reflect.Type type)
        Unsafe. Constructs a type literal manually.

    • Method Detail

      • isCapturingTypeVariablesForbidden

        private static boolean isCapturingTypeVariablesForbidden()

      • getTypeTokenTypeArgument

        private java.lang.reflect.Type getTypeTokenTypeArgument()
        Verifies that this is an instance of a direct subclass of TypeToken and returns the type argument for T in canonical form.

      • verifyNoTypeVariable

        private static void verifyNoTypeVariable​(java.lang.reflect.Type type)

      • getRawType

        public final java.lang.Class<? super T> getRawType()
        Returns the raw (non-generic) type for this type.

      • getType

        public final java.lang.reflect.Type getType()
        Gets underlying Type instance.

      • isAssignableFrom

        @Deprecated
public boolean isAssignableFrom​(java.lang.Class<?> cls)
        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
public boolean isAssignableFrom​(java.lang.reflect.Type from)
        Deprecated.
        this implementation may be inconsistent with javac for types with wildcards.
        Check if this type is assignable from the given Type.

      • isAssignableFrom

        @Deprecated
public boolean isAssignableFrom​(TypeToken<?> token)
        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 static boolean isAssignableFrom​(java.lang.reflect.Type from,
                                        java.lang.reflect.GenericArrayType to)
        Private helper function that performs some assignability checks for the provided GenericArrayType.

      • isAssignableFrom

        private static boolean isAssignableFrom​(java.lang.reflect.Type from,
                                        java.lang.reflect.ParameterizedType to,
                                        java.util.Map<java.lang.String,​java.lang.reflect.Type> typeVarMap)
        Private recursive helper function to actually do the type-safe checking of assignability.

      • typeEquals

        private static boolean typeEquals​(java.lang.reflect.ParameterizedType from,
                                  java.lang.reflect.ParameterizedType to,
                                  java.util.Map<java.lang.String,​java.lang.reflect.Type> typeVarMap)
        Checks if two parameterized types are exactly equal, under the variable replacement described in the typeVarMap.

      • buildUnsupportedTypeException

        private static java.lang.IllegalArgumentException buildUnsupportedTypeException​(java.lang.reflect.Type token,
                                                                                java.lang.Class<?>... expected)

      • matches

        private static boolean matches​(java.lang.reflect.Type from,
                               java.lang.reflect.Type to,
                               java.util.Map<java.lang.String,​java.lang.reflect.Type> typeMap)
        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()
        Overrides:
        hashCode in class java.lang.Object

      • equals

        public final boolean equals​(java.lang.Object o)
        Overrides:
        equals in class java.lang.Object

      • toString

        public final java.lang.String toString()
        Overrides:
        toString in class java.lang.Object

      • get

        public static TypeToken<?> get​(java.lang.reflect.Type type)
        Gets type literal for the given Type instance.

      • get

        public static <T> TypeToken<T> get​(java.lang.Class<T> type)
        Gets type literal for the given Class instance.

      • getParameterized

        public static TypeToken<?> getParameterized​(java.lang.reflect.Type rawType,
                                            java.lang.reflect.Type... typeArguments)
        Gets a type literal for the parameterized type represented by applying typeArguments to rawType. This is mainly intended for situations where the type arguments are not available at compile time. The following example shows how a type token for Map<K, V> can be created: 
        
 Class<K> keyClass = ...;
 Class<V> valueClass = ...;
 TypeToken<?> mapTypeToken = TypeToken.getParameterized(Map.class, keyClass, valueClass);
        As seen here the result is a 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 to get(Class) and creates a TypeToken(Class).

        Throws:
        java.lang.IllegalArgumentException - If rawType is not of type Class, or if the type arguments are invalid for the raw type

      • getArray

        public static TypeToken<?> getArray​(java.lang.reflect.Type componentType)
        Gets type literal for the array type whose elements are all instances of componentType.