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/*******************************************************************************
* Copyright (c) 2005, 2010 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;
import java.io.Serializable;
/**
* Used by various "pluggable" classes to filter objects.
* <p>
* Provisional API: This interface is part of an interim API that is still
* under development and expected to change significantly before reaching
* stability. It is available at this early stage to solicit feedback from
* pioneering adopters on the understanding that any code that uses this API
* will almost certainly be broken (repeatedly) as the API evolves.
*
* @param <T> the type of objects to be filtered
*/
public interface Filter<T> {
/**
* Return whether the specified object is "accepted" by the
* filter. The semantics of "accept" is determined by the
* contract between the client and the server.
*/
boolean accept(T o);
/**
* Singleton implemetation of the filter interface that accepts all the
* objects (i.e. it does no filtering).
*/
final class Null<S> implements Filter<S>, Serializable {
@SuppressWarnings("rawtypes")
public static final Filter INSTANCE = new Null();
@SuppressWarnings("unchecked")
public static <R> Filter<R> instance() {
return INSTANCE;
}
// ensure single instance
private Null() {
super();
}
// nothing is filtered - everything is accepted
public boolean accept(S o) {
return true;
}
@Override
public String toString() {
return "Filter.Null"; //$NON-NLS-1$
}
private static final long serialVersionUID = 1L;
private Object readResolve() {
// replace this object with the singleton
return INSTANCE;
}
}
/**
* Singleton implemetation of the filter interface that accepts none of the
* objects (i.e. it filters out all the objects).
*/
final class Opaque<S> implements Filter<S>, Serializable {
@SuppressWarnings("rawtypes")
public static final Filter INSTANCE = new Opaque();
@SuppressWarnings("unchecked")
public static <R> Filter<R> instance() {
return INSTANCE;
}
// ensure single instance
private Opaque() {
super();
}
// everything is filtered - nothing is accepted
public boolean accept(S o) {
return false;
}
@Override
public String toString() {
return "Filter.Opaque"; //$NON-NLS-1$
}
private static final long serialVersionUID = 1L;
private Object readResolve() {
// replace this object with the singleton
return INSTANCE;
}
}
/**
* Singleton implemetation of the filter interface that throws an exception
* if called.
*/
final class Disabled<S> implements Filter<S>, Serializable {
@SuppressWarnings("rawtypes")
public static final Filter INSTANCE = new Disabled();
@SuppressWarnings("unchecked")
public static <R> Filter<R> instance() {
return INSTANCE;
}
// ensure single instance
private Disabled() {
super();
}
// throw an exception
public boolean accept(S o) {
throw new UnsupportedOperationException();
}
@Override
public String toString() {
return "Filter.Disabled"; //$NON-NLS-1$
}
private static final long serialVersionUID = 1L;
private Object readResolve() {
// replace this object with the singleton
return INSTANCE;
}
}
}
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