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hjohnhjohn
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Initial proposal
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‎modules/javafx.base/src/main/java/com/sun/javafx/binding/Subscription.java‎

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/*
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* Copyright (c) 2021 Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package com.sun.javafx.binding;
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import java.util.Objects;
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import java.util.function.Consumer;
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import javafx.beans.InvalidationListener;
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import javafx.beans.value.ChangeListener;
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import javafx.beans.value.ObservableValue;
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/**
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* A subscription encapsulates how to cancel it without having
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* to keep track of how it was created.<p>
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*
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* For example:<p>
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* <pre>Subscription s = property.subscribe(System.out::println)</pre>
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* The function passed in to {@code subscribe} does not need to be stored
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* in order to clean up the subscription later.
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*/
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@FunctionalInterface
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public interface Subscription {
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/**
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* An empty subscription. Does nothing when cancelled.
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*/
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static final Subscription EMPTY = () -> {};
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/**
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* Cancels this subscription.
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*/
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void unsubscribe();
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/**
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* Combines this {@link Subscription} with the given {@code Subscription}
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* and returns a new {@code Subscription} which will cancel both when
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* cancelled.
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*
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* @param other another {@link Subscription}, cannot be null
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* @return a combined {@link Subscription} which will cancel both when
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* cancelled, never null
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*/
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default Subscription and(Subscription other) {
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Objects.requireNonNull(other);
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return () -> {
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unsubscribe();
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other.unsubscribe();
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};
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}
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/**
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* Creates a {@link Subscription} on this {@link ObservableValue} which
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* immediately provides its current value to the given {@code subscriber},
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* followed by any subsequent changes in value.
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*
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* @param subscriber a {@link Consumer} to supply with the values of this
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* {@link ObservableValue}, cannot be null
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* @return a {@link Subscription} which can be used to cancel this
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* subscription, never null
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*/
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static <T> Subscription subscribe(ObservableValue<T> observableValue, Consumer<? super T> subscriber) {
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ChangeListener<T> listener = (obs, old, current) -> subscriber.accept(current);
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subscriber.accept(observableValue.getValue()); // eagerly send current value
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observableValue.addListener(listener);
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return () -> observableValue.removeListener(listener);
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}
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/**
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* Creates a {@link Subscription} on this {@link ObservableValue} which
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* calls the given {@code runnable} whenever this {@code ObservableValue}
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* becomes invalid.
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*
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* @param runnable a {@link Runnable} to call whenever this
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* {@link ObservableValue} becomes invalid, cannot be null
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* @return a {@link Subscription} which can be used to cancel this
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* subscription, never null
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*/
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static Subscription subscribeInvalidations(ObservableValue<?> observableValue, Runnable runnable) {
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InvalidationListener listener = obs -> runnable.run();
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observableValue.addListener(listener);
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return () -> observableValue.removeListener(listener);
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}
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}

‎modules/javafx.base/src/main/java/javafx/beans/binding/ObjectBinding.java‎

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/*
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* Copyright (c) 2010, 2020, Oracle and/or its affiliates. All rights reserved.
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* Copyright (c) 2010, 2021, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
@@ -155,7 +155,10 @@ public ObservableList<?> getDependencies() {
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public final T get() {
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if (!valid) {
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value = computeValue();
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valid = true;
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if (allowValidation()) {
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valid = true;
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}
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}
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return value;
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}
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return valid;
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}
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/**
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* Returns {@code true} when this binding currently has one or more
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* listeners, otherwise {@code false}.
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*
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* @return {@code true} when this binding currently has one or more
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* listeners, otherwise {@code false}
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*/
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protected final boolean isObserved() {
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return helper != null;
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}
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/**
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* Can be overriden in extending classes to prevent a binding from becoming
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* valid. The default implementation always allows bindings to become valid.
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*
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* @return {@code true} if this binding is allowed to become valid, otherwise
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* {@code false}
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*/
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protected boolean allowValidation() {
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return true;
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}
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/**
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* Calculates the current value of this binding.
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* <p>

‎modules/javafx.base/src/main/java/javafx/beans/value/FlatMappedBinding.java‎

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/*
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* Copyright (c) 2021 Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package javafx.beans.value;
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import java.util.Objects;
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import java.util.function.Function;
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import com.sun.javafx.binding.Subscription;
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class FlatMappedBinding<S, T> extends LazyObjectBinding<T> {
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private final ObservableValue<S> source;
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private final Function<? super S, ? extends ObservableValue<? extends T>> mapper;
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private Subscription mappedSubscription = Subscription.EMPTY;
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public FlatMappedBinding(ObservableValue<S> source, Function<? super S, ? extends ObservableValue<? extends T>> mapper) {
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this.source = Objects.requireNonNull(source, "source cannot be null");
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this.mapper = Objects.requireNonNull(mapper, "mapper cannot be null");
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}
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@Override
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protected T computeValue() {
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S value = source.getValue();
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ObservableValue<? extends T> mapped = value == null ? null : mapper.apply(value);
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if (isObserved()) {
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mappedSubscription.unsubscribe();
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mappedSubscription = mapped == null ? Subscription.EMPTY : Subscription.subscribeInvalidations(mapped, this::invalidate);
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}
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return mapped == null ? null : mapped.getValue();
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}
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@Override
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protected Subscription observeInputs() {
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Subscription subscription = Subscription.subscribeInvalidations(source, this::invalidate);
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return () -> {
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subscription.unsubscribe();
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mappedSubscription.unsubscribe();
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mappedSubscription = Subscription.EMPTY;
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};
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}
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}

‎modules/javafx.base/src/main/java/javafx/beans/value/LazyObjectBinding.java‎

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/*
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* Copyright (c) 2021 Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
6+
* under the terms of the GNU General Public License version 2 only, as
7+
* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
9+
* by Oracle in the LICENSE file that accompanied this code.
10+
*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13+
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14+
* version 2 for more details (a copy is included in the LICENSE file that
15+
* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
18+
* 2 along with this work; if not, write to the Free Software Foundation,
19+
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package javafx.beans.value;
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import com.sun.javafx.binding.Subscription;
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import javafx.beans.InvalidationListener;
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import javafx.beans.binding.ObjectBinding;
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/**
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* Extends {@link ObjectBinding} with the ability to lazily register and eagerly unregister listeners on its
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* dependencies.
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*
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* @param <T> the type of the wrapped {@code Object}
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*/
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abstract class LazyObjectBinding<T> extends ObjectBinding<T> {
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private Subscription subscription;
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private boolean wasObserved;
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@Override
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public void addListener(ChangeListener<? super T> listener) {
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super.addListener(listener);
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updateSubcriptionAfterAdd();
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}
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@Override
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public void removeListener(ChangeListener<? super T> listener) {
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super.removeListener(listener);
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updateSubcriptionAfterRemove();
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}
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@Override
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public void addListener(InvalidationListener listener) {
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super.addListener(listener);
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updateSubcriptionAfterAdd();
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}
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@Override
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public void removeListener(InvalidationListener listener) {
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super.removeListener(listener);
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updateSubcriptionAfterRemove();
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}
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@Override
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protected boolean allowValidation() {
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return isObserved();
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}
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/**
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* Called after a listener was added to start observing inputs, if they're not observed already.
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*/
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private void updateSubcriptionAfterAdd() {
80+
if (!wasObserved) { // was first observer registered?
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subscription = observeInputs(); // start observing source
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/*
84+
* Although the act of registering a listener already attempts to make
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* this binding valid, allowValidation won't allow it as the binding is
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* not observed yet. This is because isObserved will not yet return true
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* when the process of registering the listener hasn't completed yet.
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*
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* As the binding must be valid after it becomes observed the first time
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* 'get' is called again.
91+
*/
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get(); // make binding valid as source wasn't tracked until now
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wasObserved = true;
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}
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}
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/**
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* Called after a listener was removed to stop observing inputs, if this was the last listener
100+
* observing this binding.
101+
*/
102+
private void updateSubcriptionAfterRemove() {
103+
if (wasObserved && !isObserved()) { // was last observer unregistered?
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subscription.unsubscribe();
105+
subscription = null;
106+
invalidate(); // make binding invalid as source is no longer tracked
107+
wasObserved = false;
108+
}
109+
}
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/**
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* Called when this binding was previously not observed and a new observer was added. Implementors must return a
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* {@link Subscription} which will be cancelled when this binding no longer has any observers.
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*
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* @return a {@link Subscription} which will be cancelled when this binding no longer has any observers, never null
116+
*/
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protected abstract Subscription observeInputs();
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}

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