FixedBatchSpliteratorBase.java

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package uk.ac.ebi.ep.data.batch;

import java.util.Comparator;
import java.util.Spliterator;
import static java.util.Spliterators.spliterator;
import java.util.function.Consumer;

/**
 *
 * @author joseph
 * @param <T>
 */
public abstract class FixedBatchSpliteratorBase<T> implements Spliterator<T> {

    private final int batchSize;
    private final int characteristics;
    private long est;

    public FixedBatchSpliteratorBase(int characteristics, int batchSize, long est) {
        characteristics |= ORDERED;

        if ((characteristics & SIZED) != 0) {
            characteristics |= SUBSIZED;
        }
        this.characteristics = characteristics;
        this.batchSize = batchSize;
        this.est = est;
    }

    public FixedBatchSpliteratorBase(int characteristics, int batchSize) {
        this(characteristics, batchSize, Long.MAX_VALUE);
    }

    public FixedBatchSpliteratorBase(int characteristics) {
        this(characteristics, 64, Long.MAX_VALUE);
        //this(characteristics, 128, Long.MAX_VALUE);
    }

    @Override
    public Spliterator<T> trySplit() {
        final HoldingConsumer<T> holder = new HoldingConsumer<>();
        if (!tryAdvance(holder)) {
            return null;
        }
        final Object[] a = new Object[batchSize];
        int j = 0;
        do {
            a[j] = holder.value;
        } while (++j < batchSize && tryAdvance(holder));
        if (est != Long.MAX_VALUE) {
            est -= j;
        }
        return spliterator(a, 0, j, characteristics());
    }

    @Override
    public Comparator<? super T> getComparator() {
        if (hasCharacteristics(SORTED)) {
            return null;
        }
        throw new IllegalStateException();
    }

    @Override
    public long estimateSize() {
        return est;
    }

    @Override
    public int characteristics() {
        return characteristics;
    }

    static final class HoldingConsumer<T> implements Consumer<T> {

        Object value;

        @Override
        public void accept(T value) {
            this.value = value;
        }
    }
}