Repeat() and Join()

RepeatJoin.java

package org.parboiled.examples.css;

import org.parboiled.BaseParser;
import org.parboiled.Rule;
import org.parboiled.annotations.BuildParseTree;

import java.util.ArrayList;
import java.util.List;

@BuildParseTree
public class RepeatJoin
    extends BaseParser<Object>
{
    Rule Repeat(final int repetitions, final Object rule)
    {
        if (repetitions <= 0)
            throw new IllegalStateException();

        if (repetitions == 1)
            return toRule(rule);

        final List<Object> l = new ArrayList<Object>(repetitions);
        for (int i = 0; i < repetitions; i++)
            l.add(rule);

        return Sequence(l.toArray());
    }

    Rule Join(final int repetitions, final Object rule, final Object separator)
    {
        if (repetitions <= 0)
            throw new IllegalStateException();

        if (repetitions == 1)
            return toRule(rule);

        final List<Object> rules = new ArrayList<Object>(repetitions * 2 - 1);
        rules.add(rule);
        for (int i = 1; i < repetitions; i++) {
            rules.add(separator);
            rules.add(rule);
        }

        return Sequence(rules.toArray());
    }
}