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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.
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///###////////////////////////////////////////////////////////////////////////
//
// Burton Computer Corporation
// http://www.burton-computer.com
//
// Copyright (c) 2018, Burton Computer Corporation
// All rights reserved.
//
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package org.javimmutable.collections;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

/**
 * Immutable implementation of both Map.Entry and JImmutableMap.Entry that uses the same equals() and hashCode() implementations as
 * documented in javadoc for Map.Entry.
 */
@Immutable
public class MapEntry
    implements JImmutableMap.Entry,
               Map.Entry
{
    @Nonnull
    protected final K key;
    protected final V value;

    public MapEntry(@Nonnull Map.Entry entry)
    {
        this(entry.getKey(), entry.getValue());
    }

    public MapEntry(@Nonnull JImmutableMap.Entry entry)
    {
        this(entry.getKey(), entry.getValue());
    }

    public MapEntry(@Nonnull K key,
                    V value)
    {
        this.key = key;
        this.value = value;
    }

    @Nonnull
    public static  MapEntry of(@Nonnull Map.Entry entry)
    {
        return new MapEntry(entry);
    }

    @Nonnull
    public static  MapEntry of(@Nonnull JImmutableMap.Entry entry)
    {
        return new MapEntry(entry);
    }

    @Nonnull
    public static  MapEntry of(@Nonnull K key,
                                           V value)
    {
        return new MapEntry(key, value);
    }

    @Nonnull
    @Override
    public K getKey()
    {
        return key;
    }

    @Override
    public V getValue()
    {
        return value;
    }

    @Override
    public V setValue(V v)
    {
        throw new UnsupportedOperationException();
    }
    
    public JImmutableMap.Entry jimmutableEntry()
    {
        return this;
    }

    public Map.Entry javaEntry()
    {
        return this;
    }
    
    @Override
    public int hashCode()
    {
        return ((key == null) ? 0 : key.hashCode()) ^
               ((value == null) ? 0 : value.hashCode());
    }

    @Override
    public boolean equals(Object o)
    {
        if (o instanceof JImmutableMap.Entry) {
            JImmutableMap.Entry jentry = (JImmutableMap.Entry)o;
            //noinspection ConstantConditions
            return ((key == null) ? (jentry.getKey() == null) : key.equals(jentry.getKey())) &&
                   ((value == null) ? (jentry.getValue() == null) : value.equals(jentry.getValue()));
        }

        if (!(o instanceof Map.Entry)) {
            return false;
        }

        Map.Entry entry2 = (Map.Entry)o;
        return ((key == null) ? (entry2.getKey() == null) : key.equals(entry2.getKey())) &&
               ((value == null) ? (entry2.getValue() == null) : value.equals(entry2.getValue()));
    }

    @Override
    public String toString()
    {
        return makeToString(this);
    }

    private static void addToString(StringBuilder sb,
                                    Object obj)
    {
        if (obj == null) {
            sb.append("null");
        } else {
            sb.append(obj);
        }
    }

    public static String makeToString(JImmutableMap.Entry entry)
    {
        StringBuilder sb = new StringBuilder();
        addToString(sb, entry);
        return sb.toString();
    }

    public static void addToString(StringBuilder sb,
                                   JImmutableMap.Entry entry)
    {
        addToString(sb, entry.getKey());
        sb.append("=");
        addToString(sb, entry.getValue());
    }

    public static  List> toMutableEntries(@Nonnull Collection> source)
    {
        return source.stream().map(e -> MapEntry.of(e)).collect(Collectors.toList());
    }

    public static  List> toImmutableEntries(@Nonnull Collection> source)
    {
        return source.stream().map(e -> MapEntry.of(e)).collect(Collectors.toList());
    }
}