Module io.helidon.common
Package io.helidon.common

Class GenericType<T>

java.lang.Object
io.helidon.common.GenericType<T>
Type Parameters:
T - the generic type parameter
All Implemented Interfaces:
Type
public class GenericType<T> extends Object implements Type
Represents a full type including generics declaration, to avoid information loss due to type erasure. Supports in-line instantiation of objects that represent generic types with actual type parameters. An object that represents any parameterized type may be obtained by sub-classing GenericType. Alternatively, an object representing a concrete parameterized type can be created using a create(Type) and manually specifying the type() actual (parameterized) type}.

For example: 

  GenericType<List<String>> stringListType = new GenericType<List<String>>() {};

Or: 

  public class MyGenericType extends GenericType<List<String>> { ... }

  ...

  MyGenericType stringListType = new MyGenericType();

Note that due to the Java type erasure limitations the parameterized type information must be specified on a subclass, not just during the instance creation. For example, the following case would throw an IllegalArgumentException: 

  public class MyGenericType<T> extends GenericType<T> { ... }

  ...

  // The type is only specified on instance, not in a sub-class
  MyGenericType<List<String>> stringListType =
          new MyGenericType<List<String>>();

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final GenericType<Object>
    OBJECT
    Generic type for Object.
    static final GenericType<String>
    STRING
    Generic type for String.

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    GenericType()
    Constructs a new generic type, deriving the generic type and class from type parameter.

  • Method Summary

    Modifier and Type
    Method
    Description
    T
    cast(Object object)
    Casts the parameter to the type of this generic type.
    static <N> GenericType<N>
    create(Class<N> clazz)
    Constructs a new generic type instance representing the given class.
    static <N> GenericType<N>
    create(Type genericType)
    Constructs a new generic type, using the provided generic type information and deriving the class.
    static <N> GenericType<N>
    create(N object)
    Constructs a new generic type instance representing the class of the given object.
    boolean
    equals(Object obj)
     
    String
    getTypeName()
     
    int
    hashCode()
     
    boolean
    isClass()
    Whether this generic type represents a simple class with no generic information.
    Class<?>
    rawType()
    Returns the object representing the class or interface that declared the type represented by this generic type instance.
    String
    toString()
     
    Type
    type()
    The type represented by this generic type instance.

    Methods inherited from class java.lang.Object

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

  • Field Details

  • Constructor Details

    • GenericType

      protected GenericType() throws IllegalArgumentException
      Constructs a new generic type, deriving the generic type and class from type parameter. Note that this constructor is protected, users should create a (usually anonymous) subclass as shown above.
      Throws:
      IllegalArgumentException - in case the generic type parameter value is not provided by any of the subclasses.

  • Method Details

    • create

      public static <N> GenericType<N> create(Type genericType) throws IllegalArgumentException
      Constructs a new generic type, using the provided generic type information and deriving the class.
      Type Parameters:
      N - generic type of the returned GenericType
      Parameters:
      genericType - the generic type
      Returns:
      new type wrapping the provided type
      Throws:
      IllegalArgumentException - if genericType is null or not an instance of Class or ParameterizedType whose raw type is an instance of Class.

    • create

      public static <N> GenericType<N> create(Class<N> clazz)
      Constructs a new generic type instance representing the given class.
      Type Parameters:
      N - generic type of the returned GenericType
      Parameters:
      clazz - the class to represent
      Returns:
      new type wrapping the provided class

    • create

      public static <N> GenericType<N> create(N object)
      Constructs a new generic type instance representing the class of the given object.
      Type Parameters:
      N - generic type of the returned GenericType
      Parameters:
      object - the object to derive the class of
      Returns:
      new type wrapping the class of the provided object

    • type

      public Type type()
      The type represented by this generic type instance.

      For new GenericType<List<String>>(){}, this would return a ParameterizedType for java.util.List<java.lang.String>.

      Returns:
      the actual type represented by this generic type instance.

    • rawType

      public Class<?> rawType()
      Returns the object representing the class or interface that declared the type represented by this generic type instance.

      For new GenericType<List<String>>(){}, this would return an interface java.util.List.

      Returns:
      the class or interface that declared the type represented by this generic type instance.

    • isClass

      public boolean isClass()
      Whether this generic type represents a simple class with no generic information.
      Returns:
      true if this is a class, false if this is a generic type (e.g. returns true for List, false for List<String>

    • cast

      public T cast(Object object) throws ClassCastException
      Casts the parameter to the type of this generic type. This is a utility method to use in stream processing etc.
      Parameters:
      object - instance to cast
      Returns:
      typed instance
      Throws:
      ClassCastException - in case the object is not of the expected type

    • getTypeName

      public String getTypeName()
      Specified by:
      getTypeName in interface Type

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • equals

      public boolean equals(Object obj)
      Overrides:
      equals in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object