ReifiedType.java

/*
 * Copyright 2009 Alin Dreghiciu.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied.
 *
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.osgi.service.blueprint.container;

/**
 * Provides access to a concrete type and its optional generic type parameters.
 *
 * <p>
 * Java 5 and later support generic types. These types consist of a raw class
 * with type parameters. This class models such a <code>Type</code> class but
 * ensures that the type is <em>reified</em>. Reification means that the Type
 * graph associated with a Java 5 <code>Type</code> instance is traversed until
 * the type becomes a concrete class. This class is available with the
 * {@link #getRawClass()} method. The optional type parameters are recursively
 * represented as Reified Types.
 *
 * <p>
 * In Java 1.4, a class has by definition no type parameters. This class
 * implementation provides the Reified Type for Java 1.4 by making the raw class
 * the Java 1.4 class and using a Reified Type based on the <code>Object</code>
 * class for any requested type parameter.
 *
 * <p>
 * A Blueprint extender implementations can subclass this class and provide
 * access to the generic type parameter graph for conversion. Such a subclass
 * must <em>reify</em> the different Java 5 <code>Type</code> instances into the
 * reified form. That is, a form where the raw Class is available with its
 * optional type parameters as Reified Types.
 *
 * @version $Revision: 7564 $
 * @Immutable
 */
public class ReifiedType
{

    private final static ReifiedType OBJECT = new ReifiedType( Object.class );

    private final Class clazz;

    /**
     * Create a Reified Type for a raw Java class without any generic type
     * parameters. Subclasses can provide the optional generic type parameter
     * information. Without subclassing, this instance has no type parameters.
     *
     * @param clazz The raw class of the Reified Type.
     */
    public ReifiedType( Class clazz )
    {
        this.clazz = clazz;
    }

    /**
     * Return the raw class represented by this type.
     *
     * The raw class represents the concrete class that is associated with a
     * type declaration. This class could have been deduced from the generics
     * type parameter graph of the declaration. For example, in the following
     * example:
     *
     * <pre>
     * Map<String, ? extends Metadata>
     * </pre>
     *
     * The raw class is the Map class.
     *
     * @return The raw class represented by this type.
     */
    public Class getRawClass()
    {
        return clazz;
    }

    /**
     * Return a type parameter for this type.
     *
     * The type parameter refers to a parameter in a generic type declaration
     * given by the zero-based index <code>i</code>.
     *
     * For example, in the following example:
     *
     * <pre>
     * Map<String, ? extends Metadata>
     * </pre>
     *
     * type parameter 0 is <code>String</code>, and type parameter 1 is
     * <code>Metadata</code>.
     *
     * <p>
     * This implementation returns a Reified Type that has <code>Object</code>
     * as class. Any object is assignable to Object and therefore no conversion
     * is then necessary. This is compatible with versions of Java language
     * prior to Java 5.
     *
     * This method should be overridden by a subclass that provides access to
     * the generic type parameter information for Java 5 and later.
     *
     * @param i The zero-based index of the requested type parameter.
     *
     * @return The <code>ReifiedType</code> for the generic type parameter at
     *         the specified index.
     */
    public ReifiedType getActualTypeArgument( int i )
    {
        return OBJECT;
    }

    /**
     * Return the number of type parameters for this type.
     *
     * <p>
     * This implementation returns <code>0</code>. This method should be
     * overridden by a subclass that provides access to the generic type
     * parameter information for Java 5 and later.
     *
     * @return The number of type parameters for this type.
	 */
	public int size() {
		return 0;
	}
}