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• Object2ObjectFunctions.java

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/*
	* Copyright (C) 2002-2022 Sebastiano Vigna
	*
	* 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 it.unimi.dsi.fastutil.objects;

import it.unimi.dsi.fastutil.Function;

/**
 * A class providing static methods and objects that do useful things with type-specific functions.
 *
 * @see it.unimi.dsi.fastutil.Function
 * @see java.util.Collections
 */
public final class Object2ObjectFunctions {
	private Object2ObjectFunctions() {
	}

	/**
	 * An immutable class representing an empty type-specific function.
	 *
	 * 

	 * This class may be useful to implement your own in case you subclass a type-specific function.
	 */
	public static class EmptyFunction extends AbstractObject2ObjectFunction implements java.io.Serializable, Cloneable {
		private static final long serialVersionUID = -7046029254386353129L;

		protected EmptyFunction() {
		}

		@Override
		public V get(final Object k) {
			return (null);
		}

		@Override
		public V getOrDefault(final Object k, final V defaultValue) {
			return defaultValue;
		}

		@Override
		public boolean containsKey(final Object k) {
			return false;
		}

		@Override
		public V defaultReturnValue() {
			return (null);
		}

		@Override
		public void defaultReturnValue(final V defRetValue) {
			throw new UnsupportedOperationException();
		}

		@Override
		public int size() {
			return 0;
		}

		@Override
		public void clear() {
		}

		@Override
		public Object clone() {
			return EMPTY_FUNCTION;
		}

		@Override
		public int hashCode() {
			return 0;
		}

		@Override
		public boolean equals(final Object o) {
			if (!(o instanceof Function)) return false;
			return ((Function)o).size() == 0;
		}

		@Override
		public String toString() {
			return "{}";
		}

		private Object readResolve() {
			return EMPTY_FUNCTION;
		}
	}

	/** An empty type-specific function (immutable). It is serializable and cloneable. */
	@SuppressWarnings("rawtypes")
	public static final EmptyFunction EMPTY_FUNCTION = new EmptyFunction();

	/**
	 * An immutable class representing a type-specific singleton function. Note that the default return
	 * value is still settable.
	 *
	 * 

	 * Note that albeit the function is immutable, its default return value may be changed.
	 *
	 * 

	 * This class may be useful to implement your own in case you subclass a type-specific function.
	 */
	public static class Singleton extends AbstractObject2ObjectFunction implements java.io.Serializable, Cloneable {
		private static final long serialVersionUID = -7046029254386353129L;
		protected final K key;
		protected final V value;

		protected Singleton(final K key, final V value) {
			this.key = key;
			this.value = value;
		}

		@Override
		public boolean containsKey(final Object k) {
			return java.util.Objects.equals(key, k);
		}

		@Override
		public V get(final Object k) {
			return java.util.Objects.equals(key, k) ? value : defRetValue;
		}

		@Override
		public V getOrDefault(final Object k, final V defaultValue) {
			return java.util.Objects.equals(key, k) ? value : defaultValue;
		}

		@Override
		public int size() {
			return 1;
		}

		@Override
		public Object clone() {
			return this;
		}
	}

	/**
	 * Returns a type-specific immutable function containing only the specified pair. The returned
	 * function is serializable and cloneable.
	 *
	 * 

	 * Note that albeit the returned function is immutable, its default return value may be changed.
	 *
	 * @param key the only key of the returned function.
	 * @param value the only value of the returned function.
	 * @return a type-specific immutable function containing just the pair {@code <key,value>}.
	 */
	public static  Object2ObjectFunction singleton(final K key, V value) {
		return new Singleton<>(key, value);
	}

	/** A synchronized wrapper class for functions. */
	public static class SynchronizedFunction implements Object2ObjectFunction, java.io.Serializable {
		private static final long serialVersionUID = -7046029254386353129L;
		protected final Object2ObjectFunction function;
		protected final Object sync;

		protected SynchronizedFunction(final Object2ObjectFunction f, final Object sync) {
			if (f == null) throw new NullPointerException();
			this.function = f;
			this.sync = sync;
		}

		protected SynchronizedFunction(final Object2ObjectFunction f) {
			if (f == null) throw new NullPointerException();
			this.function = f;
			this.sync = this;
		}

		@Override
		public V apply(final K key) {
			synchronized (sync) {
				return function.apply(key);
			}
		}

		@Override
		public int size() {
			synchronized (sync) {
				return function.size();
			}
		}

		@Override
		public V defaultReturnValue() {
			synchronized (sync) {
				return function.defaultReturnValue();
			}
		}

		@Override
		public void defaultReturnValue(final V defRetValue) {
			synchronized (sync) {
				function.defaultReturnValue(defRetValue);
			}
		}

		@Override
		public boolean containsKey(final Object k) {
			synchronized (sync) {
				return function.containsKey(k);
			}
		}

		@Override
		public V put(final K k, final V v) {
			synchronized (sync) {
				return function.put(k, v);
			}
		}

		@Override
		public V get(final Object k) {
			synchronized (sync) {
				return function.get(k);
			}
		}

		@Override
		public V getOrDefault(final Object k, final V defaultValue) {
			synchronized (sync) {
				return function.getOrDefault(k, defaultValue);
			}
		}

		@Override
		public V remove(final Object k) {
			synchronized (sync) {
				return function.remove(k);
			}
		}

		@Override
		public void clear() {
			synchronized (sync) {
				function.clear();
			}
		}

		@Override
		public int hashCode() {
			synchronized (sync) {
				return function.hashCode();
			}
		}

		@Override
		public boolean equals(final Object o) {
			if (o == this) return true;
			synchronized (sync) {
				return function.equals(o);
			}
		}

		@Override
		public String toString() {
			synchronized (sync) {
				return function.toString();
			}
		}

		private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
			synchronized (sync) {
				s.defaultWriteObject();
			}
		}
	}

	/**
	 * Returns a synchronized type-specific function backed by the given type-specific function.
	 *
	 * @param f the function to be wrapped in a synchronized function.
	 * @return a synchronized view of the specified function.
	 * @see java.util.Collections#synchronizedMap(java.util.Map)
	 */
	public static  Object2ObjectFunction synchronize(final Object2ObjectFunction f) {
		return new SynchronizedFunction<>(f);
	}

	/**
	 * Returns a synchronized type-specific function backed by the given type-specific function, using
	 * an assigned object to synchronize.
	 *
	 * @param f the function to be wrapped in a synchronized function.
	 * @param sync an object that will be used to synchronize the access to the function.
	 * @return a synchronized view of the specified function.
	 * @see java.util.Collections#synchronizedMap(java.util.Map)
	 */
	public static  Object2ObjectFunction synchronize(final Object2ObjectFunction f, final Object sync) {
		return new SynchronizedFunction<>(f, sync);
	}

	/** An unmodifiable wrapper class for functions. */
	public static class UnmodifiableFunction extends AbstractObject2ObjectFunction implements java.io.Serializable {
		private static final long serialVersionUID = -7046029254386353129L;
		protected final Object2ObjectFunction function;

		protected UnmodifiableFunction(final Object2ObjectFunction f) {
			if (f == null) throw new NullPointerException();
			this.function = f;
		}

		@Override
		public int size() {
			return function.size();
		}

		@Override
		public V defaultReturnValue() {
			return function.defaultReturnValue();
		}

		@Override
		public void defaultReturnValue(final V defRetValue) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean containsKey(final Object k) {
			return function.containsKey(k);
		}

		@Override
		public V put(final K k, final V v) {
			throw new UnsupportedOperationException();
		}

		@Override
		public V get(final Object k) {
			return function.get(k);
		}

		@Override
		@SuppressWarnings("unchecked")
		public V getOrDefault(final Object k, final V defaultValue) {
			return ((Object2ObjectFunction)function).getOrDefault(k, defaultValue);
		}

		@Override
		public V remove(final Object k) {
			throw new UnsupportedOperationException();
		}

		@Override
		public void clear() {
			throw new UnsupportedOperationException();
		}

		@Override
		public int hashCode() {
			return function.hashCode();
		}

		@Override
		public boolean equals(Object o) {
			return o == this || function.equals(o);
		}

		@Override
		public String toString() {
			return function.toString();
		}
	}

	/**
	 * Returns an unmodifiable type-specific function backed by the given type-specific function.
	 *
	 * @param f the function to be wrapped in an unmodifiable function.
	 * @return an unmodifiable view of the specified function.
	 * @see java.util.Collections#unmodifiableMap(java.util.Map)
	 */
	public static  Object2ObjectFunction unmodifiable(final Object2ObjectFunction f) {
		return new UnmodifiableFunction<>(f);
	}
}