Java Iterable Item concat(final Iterable> iterables)

Description

concat

License

Apache License

Declaration

public static <T> Iterable<T> concat(final Iterable<? extends Iterable<T>> iterables) 

Method Source Code

//package com.java2s;
/*//from w ww .  j  a  v a2s. c om
 * Copyright (C) 2015 SoftIndex LLC.
 *
 * 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.
 */

import java.util.*;

public class Main {
    public static <T> Iterable<T> concat(final Iterable<? extends Iterable<T>> iterables) {
        return new Iterable<T>() {
            @Override
            public Iterator<T> iterator() {
                return new Iterator<T>() {
                    private final Iterator<? extends Iterable<T>> iterablesIterator = iterables.iterator();
                    // we assume that iterable.iterator() cannot return null
                    private Iterator<T> currentIterator = iterablesIterator.hasNext()
                            ? iterablesIterator.next().iterator()
                            : null;

                    @Override
                    public boolean hasNext() {
                        adjustCurrentIterator();
                        return currentIterator != null;
                    }

                    @Override
                    public T next() {
                        adjustCurrentIterator();
                        if (currentIterator == null) {
                            throw new NoSuchElementException();
                        }
                        return currentIterator.next();
                    }

                    private void adjustCurrentIterator() {
                        if (currentIterator == null || currentIterator.hasNext()) {
                            return;
                        }

                        // find next non-empty iterator
                        while (true) {
                            // we assume that iterable.iterator() cannot return null
                            currentIterator = iterablesIterator.hasNext() ? iterablesIterator.next().iterator()
                                    : null;
                            if (currentIterator == null || currentIterator.hasNext()) {
                                // currentIterator == null means that we've got to the end
                                return;
                            }
                        }
                    }

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

Related

1. clear(Iterable iterable)
2. concat(Iterable... iterables)
3. concat(Iterable first, Iterable second)
4. contains(Iterable iter, Object o)
5. getFirst(final Iterable iterable)