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package org.graalvm.polyglot;
import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
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 of the type information even at runtime. For example, to create a type literal for List<String>, you can create an empty anonymous inner class:
TypeLiteral<List<String>> list = new TypeLiteral<List<String>>() {};
See Also: Since: 19.0
/**
* Represents a generic type {@code 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 of
* the type information even at runtime.
*
* <p>
* For example, to create a type literal for {@code List<String>}, you can create an empty anonymous
* inner class:
*
* <p>
* {@code TypeLiteral<List<String>> list = new TypeLiteral<List<String>>() {};}
*
*
* @since 19.0
* @see org.graalvm.polyglot.Value#as(TypeLiteral)
*/
public abstract class TypeLiteral<T> {
private final Type type;
private final Class<T> rawType;
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.
Since: 19.0
/**
* Constructs a new type literal. Derives represented class from type parameter.
*
* <p>
* 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.
*
* @since 19.0
*/
@SuppressWarnings("unchecked")
protected TypeLiteral() {
this.type = extractLiteralType(this.getClass());
this.rawType = (Class<T>) extractRawType(type);
}
private static Type extractLiteralType(@SuppressWarnings("rawtypes") Class<? extends TypeLiteral> literalClass) {
Type superType = literalClass.getGenericSuperclass();
Type typeArgument = null;
while (true) {
if (superType instanceof ParameterizedType) {
ParameterizedType parametrizedType = (ParameterizedType) superType;
if (parametrizedType.getRawType() == TypeLiteral.class) {
// found
typeArgument = parametrizedType.getActualTypeArguments()[0];
break;
} else {
throw new AssertionError("Unsupported type hierarchy for type literal.");
}
} else if (superType instanceof Class<?>) {
if (superType == TypeLiteral.class) {
typeArgument = Object.class;
break;
} else {
superType = ((Class<?>) superType).getGenericSuperclass();
}
} else {
throw new AssertionError("Unsupported type hierarchy for type literal.");
}
}
return typeArgument;
}
private static Class<?> extractRawType(Type type) {
Class<?> rawType;
if (type instanceof Class) {
rawType = (Class<?>) type;
} else if (type instanceof ParameterizedType) {
rawType = (Class<?>) ((ParameterizedType) type).getRawType();
} else if (type instanceof GenericArrayType) {
rawType = arrayTypeFromComponentType(extractRawType(((GenericArrayType) type).getGenericComponentType()));
} else {
throw new IllegalArgumentException("Unsupported type: " + type);
}
return rawType;
}
private static Class<?> arrayTypeFromComponentType(Class<?> componentType) {
return Array.newInstance(componentType, 0).getClass();
}
Returns the type literal including generic type information.
Since: 19.0
/**
* Returns the type literal including generic type information.
*
* @since 19.0
*/
public final Type getType() {
return this.type;
}
Returns the raw class type of the literal.
Since: 19.0
/**
* Returns the raw class type of the literal.
*
* @since 19.0
*/
public final Class<T> getRawType() {
return rawType;
}
Since: 19.0
/**
* @since 19.0
*/
@Override
public final boolean equals(Object obj) {
return super.equals(obj);
}
Since: 19.0
/**
* @since 19.0
*/
@Override
public final int hashCode() {
return super.hashCode();
}
Since: 19.0
/**
* @since 19.0
*/
@Override
public final String toString() {
return "TypeLiteral<" + type + ">";
}
}