org.janusgraph.util.datastructures.IterablesUtil.java Source code

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Here is the source code for org.janusgraph.util.datastructures.IterablesUtil.java

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// Copyright 2017 JanusGraph Authors
//
// 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.janusgraph.util.datastructures;

import com.google.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.common.collect.Iterables;
import com.google.common.collect.Iterators;

import javax.annotation.Nullable;
import java.util.*;

/**
 * Utility class for interacting with {@link Iterable}.
 *
 * @author Matthias Broecheler (me@matthiasb.com)
 */
public class IterablesUtil {

    public static final <O> Iterable<O> emptyIterable() {
        return new Iterable<O>() {

            @Override
            public Iterator<O> iterator() {
                return Iterators.emptyIterator();
            }

        };
    }

    public static final Predicate NO_FILTER = new NoFilter();

    public static final <E> Predicate<E> noFilter() {
        return (Predicate<E>) NO_FILTER;
    }

    private static class NoFilter<E> implements Predicate<E> {

        @Override
        public boolean apply(@Nullable E e) {
            return true;
        }
    }

    public static final <O> Iterable<O> limitedIterable(final Iterable<O> iterable, final int limit) {
        return Iterables.filter(iterable, new Predicate<O>() {

            int count = 0;

            @Override
            public boolean apply(@Nullable O o) {
                count++;
                return count <= limit;
            }
        });
    }

    public static final int size(Iterable i) {
        if (i instanceof Collection)
            return ((Collection) i).size();
        else
            return Iterables.size(i);
    }

    public static final boolean sizeLargerOrEqualThan(Iterable i, int limit) {
        if (i instanceof Collection)
            return ((Collection) i).size() >= limit;
        Iterator iter = i.iterator();
        int count = 0;
        while (iter.hasNext()) {
            iter.next();
            count++;
            if (count >= limit)
                return true;
        }
        return false;
    }

    public static <E> List<E> mergeSort(Collection<E> a, Collection<E> b, Comparator<E> comp) {
        Iterator<E> itera = a.iterator(), iterb = b.iterator();
        E heada = itera.hasNext() ? itera.next() : null;
        E headb = iterb.hasNext() ? iterb.next() : null;
        List<E> result = new ArrayList(a.size() + b.size());
        while (heada != null || headb != null) {
            E next;
            if (heada == null) {
                next = headb;
                headb = null;
            } else if (headb == null) {
                next = heada;
                heada = null;
            } else if (comp.compare(heada, headb) <= 0) {
                next = heada;
                heada = null;
            } else {
                next = headb;
                headb = null;
            }
            assert next != null;
            Preconditions.checkArgument(result.isEmpty() || comp.compare(result.get(result.size() - 1), next) <= 0,
                    "The input collections are not sorted");
            result.add(next);
            if (heada == null)
                heada = itera.hasNext() ? itera.next() : null;
            if (headb == null)
                headb = iterb.hasNext() ? iterb.next() : null;
        }
        return result;
    }

}