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Library providing immutable/persistent collection classes for
Java. While collections are immutable they provide methods for
adding and removing values by creating new modified copies of
themselves. Each copy shares almost all of its structure with
other copies to minimize memory consumption.
///###////////////////////////////////////////////////////////////////////////
//
// Burton Computer Corporation
// http://www.burton-computer.com
//
// Copyright (c) 2018, Burton Computer Corporation
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in
// the documentation and/or other materials provided with the
// distribution.
//
// Neither the name of the Burton Computer Corporation nor the names
// of its contributors may be used to endorse or promote products
// derived from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
package org.javimmutable.collections;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;
/**
* Provides static utility methods for constructing Holder instances.
*/
public class Holders
{
private static final Empty EMPTY = new Empty();
/**
* Creates an empty Holder for the specified type.
* Shares a single instance for all empty Holders to save memory.
*
* @return the Holder
*/
@SuppressWarnings("unchecked")
@Nonnull
public static Holder of()
{
return EMPTY;
}
/**
* Creates a filled Holder for the specified type and (possibly null) value.
*/
@Nonnull
public static Holder of(@Nullable V value)
{
return new Filled()
{
@Override
public V getValue()
{
return value;
}
@Override
public int hashCode()
{
return Holders.hashCode(this);
}
@Override
@SuppressWarnings("unchecked")
public boolean equals(Object o)
{
return (o instanceof Holder) && Holders.areEqual(this, (Holder)o);
}
@Override
public String toString()
{
return String.format("[%s]", value);
}
};
}
/**
* Creates an empty Holder if value is null or a filled Holder if value is non-null.
*
* @return the Holder
*/
@Nonnull
public static Holder fromNullable(@Nullable V value)
{
if (value == null) {
return of();
} else {
return of(value);
}
}
private Holders()
{
// prevent unrelated derived classes
}
private static class Empty
implements Holder
{
public boolean isEmpty()
{
return true;
}
public boolean isFilled()
{
return false;
}
public V getValue()
{
throw new UnsupportedOperationException("cannot get empty value");
}
@Override
public V getValueOrNull()
{
return null;
}
@Override
public V getValueOr(V defaultValue)
{
return defaultValue;
}
@Override
public void ifPresent(@Nonnull Consumer consumer)
{
}
@Override
public Holder map(@Nonnull Function transforminator)
{
return of();
}
@Override
public V orElse(V defaultValue)
{
return defaultValue;
}
@Override
public V orElseGet(@Nonnull Supplier supplier)
{
return supplier.get();
}
@Override
public V orElseThrow(@Nonnull Supplier supplier)
throws X
{
throw supplier.get();
}
@Override
public int hashCode()
{
return Holders.hashCode(this);
}
@Override
@SuppressWarnings("unchecked")
public boolean equals(Object o)
{
return (o instanceof Holder) && Holders.areEqual(this, (Holder)o);
}
@Override
public String toString()
{
return "[]";
}
}
public interface Filled
extends Holder
{
default boolean isEmpty()
{
return false;
}
default boolean isFilled()
{
return true;
}
@Override
default V getValueOrNull()
{
return getValue();
}
@Override
default V getValueOr(V defaultValue)
{
return getValue();
}
@Override
default void ifPresent(@Nonnull Consumer consumer)
{
consumer.accept(getValue());
}
@Override
default Holder map(@Nonnull Function transforminator)
{
return of(transforminator.apply(getValue()));
}
@Override
default V orElse(V defaultValue)
{
return getValue();
}
@Override
default V orElseGet(@Nonnull Supplier supplier)
{
return getValue();
}
@Override
default V orElseThrow(@Nonnull Supplier supplier)
throws X
{
return getValue();
}
}
public static boolean areEqual(Holder a,
Holder b)
{
if ((a == null) || (b == null)) {
return (a == null) && (b == null);
} else if (a.isEmpty()) {
return b.isEmpty();
} else if (b.isEmpty()) {
return false;
} else {
T v1 = a.getValue();
T v2 = b.getValue();
if ((v1 == null) || (v2 == null)) {
return (v1 == null) && (v2 == null);
} else {
return v1.equals(v2);
}
}
}
public static int hashCode(Holder a)
{
if (a.isEmpty()) {
return -1;
}
if (a.getValue() == null) {
return 1;
}
return a.getValue().hashCode();
}
}