org.asoem.greyfish.utils.base.Memoizer.java Source code

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Here is the source code for org.asoem.greyfish.utils.base.Memoizer.java

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/*
 * Copyright (C) 2015 The greyfish authors
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.asoem.greyfish.utils.base;

import com.google.common.base.Optional;
import com.google.common.base.Supplier;

public abstract class Memoizer<T> implements Supplier<T> {
    private Optional<T> value = Optional.absent();

    @Override
    public final T get() {
        if (!isValid(value)) {
            synchronized (this) {
                if (!isValid(value)) {
                    T t = delegate().get();
                    value = Optional.fromNullable(t);
                    loaded(t);
                    return t;
                }
            }
        }
        return value.orNull();
    }

    /**
     * This method will be called if the memoizer has loaded and stored the value {@code t} to memoize.
     *
     * @param t the new memoized value
     */
    protected void loaded(final T t) {
    }

    protected abstract Supplier<T> delegate();

    /**
     * Check if given {@code memoized} value is valid. <p>If this method returns {@code false} than the memoizer will
     * update it's memoized value using {@link #delegate()}</p>
     *
     * @param memoized the current memoized value which is {@link com.google.common.base.Optional#absent() absent} if
     *                 the memoizer has not been initialized yet.
     * @return {@code true} if the memoizer holds a valid value, {@code false} otherwise
     */
    protected abstract boolean isValid(final Optional<T> memoized);
}