FixedInterval.java

/*
    BeepBeep, an event stream processor
    Copyright (C) 2008-2016 Sylvain Hallé

    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 functions;

import ca.uqac.lif.cep.functions.StreamVariable;
import ca.uqac.lif.cep.functions.Constant;
import ca.uqac.lif.cep.functions.FunctionException;
import ca.uqac.lif.cep.functions.FunctionTree;
import ca.uqac.lif.cep.util.Booleans;
import ca.uqac.lif.cep.util.Numbers;

/**
 * Creates a compound function (a
 * {@link ca.uqac.lif.cep.functions.FunctionTree FunctionTree})
 * that checks if a number lies between two fixed bounds.
 * <p>
 * In this example, the bounds of the interval are fixed in advance;
 * more precisely, we evaluate if a number is between 0 and 2. You may also
 * want to look at the {@link Interval} example, where the bounds of the
 * interval are replaced by variables.
 * 
 * @author Sylvain Hallé
 *
 */
public class FixedInterval
{
    public static void main(String[] args) throws FunctionException
    {
        /*
         * A FunctionTree is a function object created by
         * composing multiple functions together. Here we create
         * a function f(x) that returns true if x lies between
         * 0 and 2. The TracePlaceholder objects are used to
         * refer to the arguments, with the first argument starting at 0.
         */
        FunctionTree in_interval = new FunctionTree(Booleans.and,
                new FunctionTree(Numbers.isGreaterThan,
                        StreamVariable.X,
                        Constant.ZERO), // x > 0
                        new FunctionTree(Numbers.isLessThan,
                                StreamVariable.X,
                                new Constant(2) // x < 2
                                ));
        
        /* Likewise, a function always returns an array of objects. Most
         * functions (like this one) return a single object, so the output
         * array is also of size 1. */
        Object[] value = new Object[1];
        in_interval.evaluate(new Integer[]{3}, value); // = {false}
        System.out.printf("Return value of the function: %b\n", value[0]);
        in_interval.evaluate(new Integer[]{1}, value);
        System.out.printf("Return value of the function: %b\n", value[0]);
    }
}