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Parallel programming on the go
/*
* 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 com.gh.bmd.jrt.util;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import javax.annotation.Nonnull;
/**
* Utility abstract class used to work around Java type erasure.
*
* By using class objects it is impossible to distinguish between two different generic classes.
* For example there is no way to declare a Class<List<String>> as
* opposed to Class<List<Integer>>.
* The workaround consists in forcing the inheritance from a special generic class, then inspected
* via reflection, to obtain the generic type rather than the class object.
*
* Created by davide-maestroni on 6/14/14.
*
* @param the class type.
*/
public abstract class ClassToken {
private Type mGenericType;
private Class mRawClass;
/**
* Creates a new token from the specified raw class.
*
* @param rawClass the raw class.
* @param the class type.
* @return the newly created token.
*/
@Nonnull
@SuppressWarnings("ConstantConditions")
public static ClassToken tokenOf(@Nonnull final Class rawClass) {
if (rawClass == null) {
throw new NullPointerException("the classification raw type must not be null");
}
final ClassToken classToken = new GenericClassToken();
classToken.mGenericType = rawClass;
classToken.mRawClass = rawClass;
return classToken;
}
/**
* Creates a new token from the class of the specified object.
*
* @param object the object.
* @param the class type.
* @return the newly created token.
*/
@Nonnull
@SuppressWarnings("unchecked")
public static ClassToken tokenOf(@Nonnull final TYPE object) {
return tokenOf((Class) object.getClass());
}
/**
* Casts the specified object to this token type.
*
* Note that the cast is unsafe and may raise an exception.
*
* @param object the object to cast.
* @return the casted object.
*/
@SuppressWarnings("unchecked")
public final TYPE cast(final Object object) {
return (TYPE) object;
}
/**
* Gets the generic type of this token.
*
* @return the generic type.
* @throws java.lang.IllegalStateException if this class does not correctly extend a class
* token.
*/
@Nonnull
public final Type getGenericType() {
if (mGenericType == null) {
Class subClass = getClass();
Class superClass = subClass.getSuperclass();
while (!ClassToken.class.equals(superClass)) {
subClass = superClass;
superClass = subClass.getSuperclass();
}
final Type type = subClass.getGenericSuperclass();
if (type instanceof ParameterizedType) {
final ParameterizedType paramType = (ParameterizedType) type;
mGenericType = paramType.getActualTypeArguments()[0];
} else {
throw new IllegalStateException(
"the class does not correctly extend a class token: "
+ getClass().getName());
}
}
return mGenericType;
}
/**
* Gets the raw class of this token.
*
* @return the raw class.
* @throws java.lang.IllegalStateException if this class does not correctly extend a class
* token.
*/
@Nonnull
@SuppressWarnings("unchecked")
public final Class getRawClass() {
if (mRawClass == null) {
final Type type = getGenericType();
if (type instanceof Class) {
mRawClass = ((Class) type);
} else if (type instanceof ParameterizedType) {
mRawClass = ((Class) ((ParameterizedType) type).getRawType());
} else {
throw new IllegalStateException(
"the class does not correctly extend a class token: "
+ getClass().getName());
}
}
return mRawClass;
}
@Override
public int hashCode() {
return getRawClass().hashCode();
}
@Override
public boolean equals(final Object o) {
if (this == o) {
return true;
}
if (!(o instanceof ClassToken)) {
return false;
}
final ClassToken that = (ClassToken) o;
return getRawClass().equals(that.getRawClass());
}
/**
* Checks if this token raw class is equal to or is a superclass of the specified one.
*
* @param other the class token to compare.
* @return whether this token raw class is equal to or is a superclass.
* @throws java.lang.IllegalStateException if this class does not correctly extend a class
* token.
*/
public final boolean isAssignableFrom(@Nonnull final ClassToken other) {
return getRawClass().isAssignableFrom(other.getRawClass());
}
/**
* Checks if this token raw class represents an interface.
*
* @return whether this token raw class is an interface.
* @throws java.lang.IllegalStateException if this class does not correctly extend a class
* token.
*/
public final boolean isInterface() {
return getRawClass().isInterface();
}
/**
* Generic class token implementation.
*
* @param the class type.
*/
private static class GenericClassToken extends ClassToken {
}
}