org.opencastproject.util.data.VCell Maven / Gradle / Ivy
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* Licensed to The Apereo Foundation under one or more contributor license
* agreements. See the NOTICE file distributed with this work for additional
* information regarding copyright ownership.
*
*
* The Apereo Foundation licenses this file to you under the Educational
* Community 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://opensource.org/licenses/ecl2.txt
*
* 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.opencastproject.util.data;
import static org.opencastproject.util.EqualsUtil.ne;
import static org.opencastproject.util.RequireUtil.notNull;
import static org.opencastproject.util.data.Cells.fcell;
import static org.opencastproject.util.data.Tuple.tuple;
/**
* Value cell, a mutable data container.
*
* Cells provide a pattern that reverses the listener pattern. Instead of propagating changes of a value to registered
* listeners via callbacks, the dependent object just holds a reference to a cell and pulls the value when needed.
*
* Cells must not contain null!
*
* @param
* the value type
*/
public final class VCell extends Cell {
private volatile A a;
private int change;
private final boolean stable;
private final Object lock = new Object();
public VCell(A a, boolean stable) {
this.a = notNull(a, "a");
this.stable = stable;
change = 1;
}
/** Constructor function. */
public static VCell cell(A a) {
return new VCell(a, true);
}
/** Create a cell containing none. */
public static VCell> ocell() {
return cell(Option. none());
}
/** Get the cell's value. */
@Override
public A get() {
return a;
}
@Override
protected Tuple change() {
synchronized (lock) {
if (!stable)
change += 1;
return tuple(a, (Object) change);
}
}
/** Set the cell's value. */
public void set(A a) {
synchronized (lock) {
if (ne(a, this.a)) {
this.a = a;
change += 1;
}
}
}
public Cell lift(Function f) {
return fcell(this, f);
}
}