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A library that facilitates the use of the Guava API under JDK 8.
There is a newer version: 2.0.0
package org.bitbucket.cowwoc.guava.stream;

import com.google.common.collect.ImmutableTable;
import com.google.common.collect.Table;
import java.util.Comparator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collector.Characteristics;
import org.bitbucket.cowwoc.preconditions.Preconditions;

/**
 * Builds a stream {@link Collector} that returns an {@link ImmutableTable}.
 * 
 * @author Gili Tzabari
 * @param  the type of the input elements
 * @param  the type of rows stored in the table
 * @param  the type of columns stored in the table
 * @param  the type of values stored in the table
 */
public final class ImmutableTableCollectorBuilder
	extends TableCollectorBuilder>
{
	private Comparator rowSortingOrder;
	private Comparator columnSortingOrder;

	/**
	 * Creates a new builder.
	 * 

	 * @param rowMapper       a function that transforms the input into table rows
	 * @param columnMapper    a function that transforms the input into table columns
	 * @param valueMapper     a function that transforms the input into table values
	 * @param supplier        a function which returns a new, empty {@code Table} into which
	 *                        intermediate results will be added
	 * @param characteristics the collector characteristics
	 * @throws NullPointerException if any of the arguments are null
	 */
	public ImmutableTableCollectorBuilder(Function rowMapper,
		Function columnMapper, Function valueMapper,
		Supplier> supplier, Characteristics... characteristics)
	{
		super(rowMapper, columnMapper, valueMapper, supplier, ImmutableTable::copyOf, characteristics);
	}

	/**
	 * Sorts the table rows.
	 * 

	 * WARNING: Invoking this method overrides the
	 * {@link #finisher(java.util.function.Function) finisher}.
	 * 

	 * @param comparator specifies the row sorting order
	 * @return this
	 * @throws NullPointerException if comparator is null
	 */
	public ImmutableTableCollectorBuilder orderRowsBy(
		Comparator comparator) throws NullPointerException
	{
		Preconditions.requireThat(comparator, "comparator").isNotNull();
		this.rowSortingOrder = comparator;
		return this;
	}

	/**
	 * @return the row sorting order
	 */
	public Comparator orderRowsBy()
	{
		return rowSortingOrder;
	}

	/**
	 * Sorts the table columns.
	 * 

	 * WARNING: Invoking this method overrides the
	 * {@link #finisher(java.util.function.Function) finisher}.
	 * 
	 * @param comparator specifies the column sorting order
	 * @return this
	 * @throws NullPointerException if comparator is null
	 */
	public ImmutableTableCollectorBuilder orderColumnsBy(
		Comparator comparator) throws NullPointerException
	{
		Preconditions.requireThat(comparator, "comparator").isNotNull();
		this.columnSortingOrder = comparator;
		return this;
	}

	/**
	 * @return the column sorting order
	 */
	public Comparator orderColumnsBy()
	{
		return columnSortingOrder;
	}

	/**
	 * {@inheritDoc} WARNING: Invoking this method overrides the
	 * {@link #orderRowsBy(java.util.Comparator) row} and
	 * {@link #orderColumnsBy(java.util.Comparator) column} sort order.
	 */
	@Override
	public ImmutableTableCollectorBuilder finisher(
		Function, ImmutableTable> finisher)
		throws NullPointerException
	{
		this.rowSortingOrder = null;
		this.columnSortingOrder = null;
		super.finisher(finisher);
		return this;
	}

	@Override
	public Collector> build()
	{
		if (rowSortingOrder != null || columnSortingOrder != null)
		{
			super.finisher(value ->
			{
				ImmutableTable.Builder builder = ImmutableTable.builder().
					putAll(value);
				if (rowSortingOrder != null)
					builder.orderRowsBy(rowSortingOrder);
				if (columnSortingOrder != null)
					builder.orderColumnsBy(columnSortingOrder);
				return builder.build();
			});
		}
		return super.build();
	}
}