ReifiedType.java

/*
 * Copyright (c) OSGi Alliance (2008, 2009). All Rights Reserved.
 *
 * 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.apache.karaf.shell.support.converter;

/**
 * Provides access to a concrete type and its optional generic type arguments.
 *
 * Java 5 and later support generic types. These types consist of a raw class
 * with type arguments. 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. In Java 1.4 a class has no
 * arguments. This concrete class implements the Reified Type for Java 1.4.
 *
 * In Java 1.4, this class works with non-generic types. In that cases, a
 * Reified Type provides access to the class and has zero type arguments, though
 * a subclass that provide type arguments should be respected. Blueprint
 * extender implementations can subclass this class and provide access to the
 * generics type graph if used in a 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 arguments as Reified Types.
 */
@SuppressWarnings("rawtypes")
public class ReifiedType {
	final static ReifiedType ALL = new ReifiedType(Object.class);

	
	private final Class clazz;

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

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

	/**
	 * Access to a type argument.
	 *
	 * The type argument refers to a argument in a generic type declaration
	 * given by index <code>i</code>. This method returns a Reified Type that
	 * has Object as class when no generic type information is available. Any
	 * object is assignable to Object and therefore no conversion is then
	 * necessary, this is compatible with older Javas than 5. For this reason,
	 * the implementation in this class always returns the
	 * <code>Object</code> class, regardless of the given index.
	 *
	 * This method should be overridden by a subclass that provides access to
	 * the generic information.
	 *
	 * For example, in the following example:
	 *
	 * <pre>
	 * Map<String, Object> map;
	 * </pre>
	 *
	 * The type argument 0 is <code>String</code>, and type argument 1 is
	 * <code>Object</code>.
	 *
	 * @param i
	 *            The index of the type argument
	 * @return <code>ReifiedType</code>, subclasses must override this and return the generic argument at index <code>i</code>
	 */
	public ReifiedType getActualTypeArgument(int i) {
		return ALL;
	}

	/**
	 * Return the number of type arguments.
	 *
	 * This method should be overridden by a subclass to support Java 5 types.
	 *
	 * @return 0, subclasses must override this and return the number of generic
	 *         arguments
	 */
	public int size() {
		return 0;
	}
}