Iterables.java

/*
 * Copyright (c) 2002-2017 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * 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 org.neo4j.driver.internal.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

import org.neo4j.driver.v1.util.Function;

public class Iterables
{
    public static int count( Iterable<?> it )
    {
        if ( it instanceof Collection ) { return ((Collection) it).size(); }
        int size = 0;
        for ( Object o : it )
        {
            size++;
        }
        return size;
    }

    public static <T> List<T> asList( Iterable<T> it )
    {
        if ( it instanceof List ) { return (List<T>) it; }
        List<T> list = new ArrayList<>();
        for ( T t : it )
        {
            list.add( t );
        }
        return list;
    }

    public static <T> T single( Iterable<T> it )
    {
        Iterator<T> iterator = it.iterator();
        if ( !iterator.hasNext() )
        {
            throw new IllegalArgumentException( "Given iterable is empty" );
        }
        T result = iterator.next();
        if ( iterator.hasNext() )
        {
            throw new IllegalArgumentException( "Given iterable contains more than one element: " + it );
        }
        return result;
    }

    public static Map<String, String> map( String ... alternatingKeyValue )
    {
        Map<String, String> out = new HashMap<>();
        for ( int i = 0; i < alternatingKeyValue.length; i+=2 )
        {
            out.put( alternatingKeyValue[i], alternatingKeyValue[i+1] );
        }
        return out;
    }

    public static <A,B> Iterable<B> map(final Iterable<A> it, final Function<A,B> f)
    {
        return new Iterable<B>()
        {
            @Override
            public Iterator<B> iterator()
            {
                final Iterator<A> aIterator = it.iterator();
                return new Iterator<B>()
                {
                    @Override
                    public boolean hasNext()
                    {
                        return aIterator.hasNext();
                    }

                    @Override
                    public B next()
                    {
                        return f.apply( aIterator.next() );
                    }

                    @Override
                    public void remove()
                    {
                        aIterator.remove();
                    }
                };
            }
        };
    }

    public static <K, A, B> Map<K,B> mapValues( Map<K,A> map, Function<A,B> f )
    {
        HashMap<K,B> transformed = new HashMap<>( map.size() );
        for ( Entry<K,A> entry : map.entrySet() )
        {
            transformed.put( entry.getKey(), f.apply( entry.getValue() ) );
        }
        return transformed;
    }
}