blob: 2aa982a3bbf32a66de1fdcd8fd7edd78b5c5ffb3 (
plain) (
tree)
|
|
/*******************************************************************************
* Copyright (c) 2005, 2012 Oracle. All rights reserved.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0, which accompanies this distribution
* and is available at http://www.eclipse.org/legal/epl-v10.html.
*
* Contributors:
* Oracle - initial API and implementation
******************************************************************************/
package org.eclipse.jpt.common.utility.internal;
import java.io.Serializable;
/**
* Used by various "pluggable" classes to transform objects.
* Transform an object of type <code>T1</code> to an object of type
* <code>T2</code>.
*
* @param <T1> the type of the object passed to the transformer
* @param <T2> the type of the object returned by the transformer
*/
public interface Transformer<T1, T2> {
/**
* Return the transformed object.
* The semantics of "transform" is determined by the
* contract between the client and the server.
*/
T2 transform(T1 o);
/**
* A "null" transformer will perform no transformation at all;
* it will simply return the object "untransformed".
*/
final class Null<S1, S2>
implements Transformer<S1, S2>, Serializable
{
@SuppressWarnings("rawtypes")
public static final Transformer INSTANCE = new Null();
@SuppressWarnings("unchecked")
public static <R1, R2> Transformer<R1, R2> instance() {
return INSTANCE;
}
// ensure single instance
private Null() {
super();
}
// simply return the object, unchanged
@SuppressWarnings("unchecked")
public S2 transform(S1 o) {
return (S2) o;
}
@Override
public String toString() {
return StringTools.buildSingletonToString(this);
}
private static final long serialVersionUID = 1L;
private Object readResolve() {
// replace this object with the singleton
return INSTANCE;
}
}
/**
* A "disabled" transformer will throw an exception if
* {@link #transform(Object)} is called. This is useful in situations
* where a transformer is optional and the default transformer should
* not be used.
*/
final class Disabled<S1, S2>
implements Transformer<S1, S2>, Serializable
{
@SuppressWarnings("rawtypes")
public static final Transformer INSTANCE = new Disabled();
@SuppressWarnings("unchecked")
public static <R1, R2> Transformer<R1, R2> instance() {
return INSTANCE;
}
// ensure single instance
private Disabled() {
super();
}
// throw an exception
public S2 transform(S1 o) {
throw new UnsupportedOperationException();
}
@Override
public String toString() {
return StringTools.buildSingletonToString(this);
}
private static final long serialVersionUID = 1L;
private Object readResolve() {
// replace this object with the singleton
return INSTANCE;
}
}
}
|
