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/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
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*
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* Copyright 2011 OpenConcerto, by ILM Informatique. All rights reserved.
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*
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* The contents of this file are subject to the terms of the GNU General Public License Version 3
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* only ("GPL"). You may not use this file except in compliance with the License. You can obtain a
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* copy of the License at http://www.gnu.org/licenses/gpl-3.0.html See the License for the specific
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* language governing permissions and limitations under the License.
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*
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* When distributing the software, include this License Header Notice in each file.
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*/
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package org.openconcerto.utils.function;
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import java.util.Objects;
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import java.util.function.Supplier;
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import net.jcip.annotations.GuardedBy;
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import net.jcip.annotations.ThreadSafe;
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/**
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* A Supplier that always returns the same value. Functional in the sense, that for the same input
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* (indeed none in this case) it returns the same output.
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*
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* @author sylvain
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* @param <T> the type of results supplied by this supplier.
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*/
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@ThreadSafe
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public abstract class FunctionalSupplier<T> implements Supplier<T> {
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// Not an interface to restrict implementations (even inadvertently with the :: notation)
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@ThreadSafe
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static final class LazyValue<T> extends FunctionalSupplier<T> {
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private final Supplier<T> supplier;
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@GuardedBy("this")
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private boolean set;
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@GuardedBy("this")
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private T value;
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LazyValue(final Supplier<T> supplier) {
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super();
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this.supplier = Objects.requireNonNull(supplier);
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this.set = false;
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}
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@Override
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public synchronized T get() {
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if (!this.set) {
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this.value = this.supplier.get();
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this.set = true;
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}
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return this.value;
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}
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@Override
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public String toString() {
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return this.getClass().getSimpleName() + " for " + this.supplier;
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}
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}
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static public final <U> FunctionalSupplier<U> get(Supplier<U> orig) {
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return orig instanceof FunctionalSupplier ? (FunctionalSupplier<U>) orig : new LazyValue<>(orig);
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}
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static public final <U> ConstantSupplier<U> getConstant(U value) {
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return new ConstantSupplier<>(value);
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}
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// not public to restrict implementations
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FunctionalSupplier() {
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}
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}
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