RandomBoolean.java

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/*
    Synthia, a data structure generator
    Copyright (C) 2019-2020 Laboratoire d'informatique formelle
    Université du Québec à Chicoutimi, Canada
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published
    by the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
 
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.
 
    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package ca.uqac.lif.synthia.random;
 
import ca.uqac.lif.synthia.Picker;
import ca.uqac.lif.synthia.Reactive;
import ca.uqac.lif.synthia.Shrinkable;
import ca.uqac.lif.synthia.util.Constant;
import ca.uqac.lif.synthia.util.NothingPicker;
 
/**
 * Picks a Boolean value. This class actually implements a Bernoulli
 * trial, with the possibility of setting the probability of success
 * <i>p</i>.
 * 
 * @ingroup API
 */
public class RandomBoolean extends RandomPicker<Boolean> implements Shrinkable<Boolean>, Reactive<Float,Boolean>
{
    /**
     * The probability of picking <tt>true</tt>
     */
    protected float m_trueProbability;
    
    /**
     * Creates a new instance of the picker
     * @param true_probability The probability of picking <tt>true</tt>;
     * must be between 0 and 1.
     */
    public RandomBoolean(/*@ non_null @*/ Number true_probability)
    {
        super();
        m_trueProbability = true_probability.floatValue();
    }
 
    /**
     * Private constructor used in the duplicate method.
     * @param true_probability The probability of picking <tt>true</tt>.
     * @param seed The initial seed of the random genarator.
     * @param random The random generator.
     */
    private RandomBoolean(Number true_probability, int seed, Random random)
    {
        m_trueProbability = true_probability.floatValue();
        m_seed = seed;
        m_random = random;
    }
 
    /**
     * Creates a new instance of the picker, with a 50-50 chance of
     * producing <tt>true</tt> or <tt>false</tt>
     */
    public RandomBoolean()
    {
        this(0.5);
    }
    
    /**
     * Sets the probability for this picker to return <tt>true</tt>.
     * @param p The probability of picking <tt>true</tt>.
     */
    @Override
    public void tell(Float p)
    {
        m_trueProbability = p;
    }
 
    /**
     * Picks a random boolean. Typically, this method is expected to return non-null
     * objects; a <tt>null</tt> return value is used to signal that no more
     * objects will be produced. That is, once this method returns
     * <tt>null</tt>, it should normally return <tt>null</tt> on all subsequent
     * calls.
     * @return The random boolean.
     */
    @Override
    public Boolean pick()
    {
        return m_random.nextFloat() <= m_trueProbability;
    }
 
 
    /**
     * Creates a copy of the RandomBoolean picker.
     * @param with_state If set to <tt>false</tt>, the returned copy is set to
     * the class' initial state (i.e. same thing as calling the picker's
     * constructor). If set to <tt>true</tt>, the returned copy is put into the
     * same internal state as the object it is copied from.
     * @return The copy of the RandomBoolean picker
     */
    @Override
    public RandomBoolean duplicate(boolean with_state) 
    {
        RandomBoolean copy = new RandomBoolean(m_trueProbability, m_seed, m_random.Duplicate());
 
        if (!with_state)
        {
            copy.reset();
        }
 
        return copy;
    }
 
    @Override
    public Shrinkable<Boolean> shrink(Boolean o, Picker<Float> decision, float magnitude)
    {
        // We assume an ordering of Booleans where false < true
        if (o)
        {
            return new Constant<Boolean>(false);
        }
        return new NothingPicker<Boolean>();
    }
 
    @Override
    public Shrinkable<Boolean> shrink(Boolean o)
    {
        return shrink(o, RandomFloat.instance, 1);
    }
}