CollectionToArray.java

/*
 * Copyright 2010-2015 JetBrains s.r.o.
 *
 * 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 kotlin.jvm.internal;

import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;

public class CollectionToArray {
    // Based on the implementation from AbstractCollection

    @SuppressWarnings("SSBasedInspection")
    private static final Object[] EMPTY_OBJECT_ARRAY = new Object[0];

    public static Object[] toArray(Collection<?> collection) {
        int size = collection.size();
        if (size == 0) return EMPTY_OBJECT_ARRAY;

        Object[] r = new Object[size];
        Iterator<?> it = collection.iterator();
        for (int i = 0; i < size; i++) {
            if (!it.hasNext()) {
                // fewer elements than expected
                return Arrays.copyOf(r, i);
            }
            r[i] = it.next();
        }
        return it.hasNext() ? finishToArray(r, it) : r;
    }

    public static <T, E> T[] toArray(Collection<E> collection, T[] a) {
        // Estimate size of array; be prepared to see more or fewer elements
        int size = collection.size();
        T[] r = a.length >= size ? a :
                (T[])java.lang.reflect.Array
                        .newInstance(a.getClass().getComponentType(), size);
        Iterator<E> it = collection.iterator();

        for (int i = 0; i < r.length; i++) {
            if (! it.hasNext()) { // fewer elements than expected
                if (a != r)
                    return Arrays.copyOf(r, i);
                r[i] = null; // null-terminate
                return r;
            }
            r[i] = (T)it.next();
        }
        return it.hasNext() ? finishToArray(r, it) : r;
    }

    private static <T> T[] finishToArray(T[] r, Iterator<?> it) {
        int i = r.length;
        while (it.hasNext()) {
            int cap = r.length;
            if (i == cap) {
                int newCap = ((cap / 2) + 1) * 3;
                if (newCap <= cap) { // integer overflow
                    if (cap == Integer.MAX_VALUE)
                        throw new OutOfMemoryError
                                ("Required array size too large");
                    newCap = Integer.MAX_VALUE;
                }
                r = Arrays.copyOf(r, newCap);
            }
            r[i++] = (T)it.next();
        }
        // trim if overallocated
        return (i == r.length) ? r : Arrays.copyOf(r, i);
    }

    private CollectionToArray() {
    }
}