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/*
* Copyright 2015 Open Networking Laboratory
*
* 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.onosproject.store.service;
import java.util.function.Function;
import org.joda.time.DateTime;
import com.google.common.base.MoreObjects;
import com.google.common.base.Objects;
/**
* Versioned value.
*
* @param <V> value type.
*/
public class Versioned<V> {
private final V value;
private final long version;
private final long creationTime;
/**
* Constructs a new versioned value.
* @param value value
* @param version version
* @param creationTime milliseconds of the creation event
* from the Java epoch of 1970-01-01T00:00:00Z
*/
public Versioned(V value, long version, long creationTime) {
this.value = value;
this.version = version;
this.creationTime = creationTime;
}
/**
* Constructs a new versioned value.
* @param value value
* @param version version
*/
public Versioned(V value, long version) {
this(value, version, System.currentTimeMillis());
}
/**
* Returns the value.
*
* @return value.
*/
public V value() {
return value;
}
/**
* Returns the version.
*
* @return version
*/
public long version() {
return version;
}
/**
* Returns the system time when this version was created.
* <p>
* Care should be taken when relying on creationTime to
* implement any behavior in a distributed setting. Due
* to the possibility of clock skew it is likely that
* even creationTimes of causally related versions can be
* out or order.
* @return creation time
*/
public long creationTime() {
return creationTime;
}
/**
* Maps this instance into another after transforming its
* value while retaining the same version and creationTime.
* @param transformer function for mapping the value
* @param <U> value type of the returned instance
* @return mapped instance
*/
public <U> Versioned<U> map(Function<V, U> transformer) {
return new Versioned<>(transformer.apply(value), version, creationTime);
}
/**
* Returns the value of the specified Versioned object if non-null or else returns
* a default value.
* @param versioned versioned object
* @param defaultValue default value to return if versioned object is null
* @param <U> type of the versioned value
* @return versioned value or default value if versioned object is null
*/
public static <U> U valueOrElse(Versioned<U> versioned, U defaultValue) {
return versioned == null ? defaultValue : versioned.value();
}
@Override
public int hashCode() {
return Objects.hashCode(value, version, creationTime);
}
@Override
public boolean equals(Object other) {
if (!(other instanceof Versioned)) {
return false;
}
Versioned<V> that = (Versioned) other;
return Objects.equal(this.value, that.value) &&
Objects.equal(this.version, that.version) &&
Objects.equal(this.creationTime, that.creationTime);
}
@Override
public String toString() {
return MoreObjects.toStringHelper(this)
.add("value", value)
.add("version", version)
.add("creationTime", new DateTime(creationTime))
.toString();
}
}
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