com.github.richardballard.arbeeutils.misc.OnChangeNotifier Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of arbee-utils Show documentation

A collection of utilities that I find useful across various projects

There is a newer version: 2.0

/*
 * (C) Copyright 2016 Richard Ballard.
 *
 * 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.github.richardballard.arbeeutils.misc;

import com.google.common.annotations.VisibleForTesting;
import net.jcip.annotations.ThreadSafe;
import org.jetbrains.annotations.NotNull;

import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Supplier;

/**
 * Instances of this class have a supplier of values and hold the 'last known value' from that supplier.  They are
 * also constructed with a consumer that is notified when a change in value occurs.
 */
@ThreadSafe
public class OnChangeNotifier {

    @NotNull
    private final ChangeChecker changeChecker;

    @NotNull
    private final Consumer> changedValueConsumer;

    @VisibleForTesting
    OnChangeNotifier(@NotNull final ChangeChecker changeChecker,
                     @NotNull final Consumer> changedValueConsumer) {
        assert changeChecker != null;
        assert changedValueConsumer != null;

        this.changeChecker = changeChecker;
        this.changedValueConsumer = changedValueConsumer;
    }

    public OnChangeNotifier(@NotNull final Supplier> valueSupplier,
                            @NotNull final Consumer> changedValueConsumer) {
        this(new ChangeChecker(valueSupplier),
             changedValueConsumer);

        assert valueSupplier != null;
        assert changedValueConsumer != null;
    }

    public void checkForChange() {
        changeChecker.checkForChange().ifPresent(changedValueConsumer::accept);
    }

}