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A general programming library in Java
There is a newer version: 1.10.1
/*
 * Copyright (C) 2016 HaiYang Li
 *
 * 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 com.landawn.abacus.util.stream;

import static com.landawn.abacus.util.stream.StreamBase.checkFromToIndex;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

import com.landawn.abacus.util.Array;
import com.landawn.abacus.util.N;

/**
 * 
 * @since 0.8
 * 
 * @author Haiyang Li
 */
public abstract class ExIterator extends com.landawn.abacus.util.ImmutableIterator implements SkippableIterator {
    @SuppressWarnings("rawtypes")
    public static final ExIterator EMPTY = new QueuedIterator(0) {
        @Override
        public boolean hasNext() {
            return false;
        }

        @Override
        public Object next() {
            throw new NoSuchElementException();
        }

        @Override
        public long count() {
            return 0;
        }

        @Override
        public void skip(long n) {
            // Do nothing.
        }
    };

    public static  ExIterator empty() {
        return EMPTY;
    }

    public static  ExIterator of(final T[] a) {
        return a == null ? EMPTY : of(a, 0, a.length);
    }

    public static  ExIterator of(final T[] a, final int fromIndex, final int toIndex) {
        checkFromToIndex(fromIndex, toIndex, a.length);

        if (fromIndex == toIndex) {
            return EMPTY;
        }

        return new QueuedIterator(toIndex - fromIndex) {
            int cursor = fromIndex;

            @Override
            public boolean hasNext() {
                return cursor < toIndex;
            }

            @Override
            public T next() {
                if (cursor >= toIndex) {
                    throw new NoSuchElementException();
                }

                return a[cursor++];
            }

            @Override
            public long count() {
                return toIndex - cursor;
            }

            @Override
            public void skip(long n) {
                cursor = n < toIndex - cursor ? cursor + (int) n : toIndex;
            }

            @Override
            public  A[] toArray(A[] b) {
                b = b.length >= toIndex - cursor ? b : (A[]) N.newArray(b.getClass().getComponentType(), toIndex - cursor);

                N.copy(a, cursor, b, 0, toIndex - cursor);

                return b;
            }
        };
    }

    public static  ExIterator of(final Iterator iter) {
        if (iter instanceof ExIterator) {
            return ((ExIterator) iter);
        }

        return new ExIterator() {
            @Override
            public boolean hasNext() {
                return iter.hasNext();
            }

            @Override
            public T next() {
                return iter.next();
            }
        };
    }

    public static  ExIterator of(final Collection c) {
        final Iterator iter = c.iterator();

        return new QueuedIterator(c.size()) {
            @Override
            public boolean hasNext() {
                return iter.hasNext();
            }

            @Override
            public T next() {
                return iter.next();
            }
            //
            //            @Override
            //            public long count() {
            //                return c.size();
            //            }
            //
            //            @Override
            //            public  A[] toArray(A[] a) {
            //                return c.toArray(a);
            //            }
        };
    }

    @Override
    public long count() {
        long result = 0;

        while (hasNext()) {
            next();
            result++;
        }

        return result;
    }

    @Override
    public void skip(long n) {
        while (n > 0 && hasNext()) {
            next();
            n--;
        }
    }

    public  A[] toArray(A[] a) {
        final List list = new ArrayList<>();

        while (hasNext()) {
            list.add((A) next());
        }

        if (a.length >= list.size()) {
            return list.toArray(a);
        } else {
            return list.toArray((A[]) Array.newInstance(a.getClass().getComponentType(), list.size()));
        }
    }

    static abstract class QueuedIterator extends ExIterator {
        private final int max;

        QueuedIterator(int max) {
            this.max = max;
        }

        public int max() {
            return max;
        }
    }
}