Switch.java

/*
 * Strongback
 * Copyright 2015, Strongback and individual contributors by the @authors tag.
 * See the COPYRIGHT.txt in the distribution for a full listing of individual
 * contributors.
 *
 * Licensed under the MIT License; you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 * http://opensource.org/licenses/MIT
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.strongback.components;

import java.util.Objects;

import org.strongback.annotation.ThreadSafe;


/**
 * A switch is any readable device that has an active state when it is triggered and an inactive state when it isn't.
 *
 * @author Zach Anderson
 */
@ThreadSafe
@FunctionalInterface
public interface Switch {
    /**
     * Checks if this switch is triggered.
     *
     * @return {@code true} if this switch was triggered, or {@code false} otherwise
     */
    public boolean isTriggered();

    /**
     * Create a switch that is always triggered.
     * @return the always-triggered switch; never null
     */
    public static Switch alwaysTriggered() {
        return ()->true;
    }

    /**
     * Create a switch that is never triggered.
     * @return the never-triggered switch; never null
     */
    public static Switch neverTriggered() {
        return ()->false;
    }

    /**
     * Return a new switch that is only triggered when <em>both</em> switches are triggered.
     * @param switch1 the first switch; may not be null
     * @param switch2 the second switch; may not be null
     * @return the logical AND of the two switches; never null
     */
    public static Switch and( Switch switch1, Switch switch2 ) {
        Objects.requireNonNull(switch1,"The first switch may not be null");
        Objects.requireNonNull(switch2,"The second switch may not be null");
        if ( switch1 == switch2 ) return switch1;
        return ()->switch1.isTriggered() && switch2.isTriggered();
    }

    /**
     * Return a new switch that is only triggered when <em>either</em> switch is triggered.
     * @param switch1 the first switch; may not be null
     * @param switch2 the second switch; may not be null
     * @return the logical OR of the two switches; never null
     */
    public static Switch or( Switch switch1, Switch switch2 ) {
        Objects.requireNonNull(switch1,"The first switch may not be null");
        Objects.requireNonNull(switch2,"The second switch may not be null");
        if ( switch1 == switch2 ) return switch1;
        return ()->switch1.isTriggered() || switch2.isTriggered();
    }
}