org.sql.generation.api.grammar.booleans.Predicate Maven / Gradle / Ivy

/*
 * Copyright (c) 2010, Stanislav Muhametsin. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
 * 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.sql.generation.api.grammar.booleans;

/**
 * A common interfaces for predicates (boolean expressions not containing other boolean expressions).
 * 
 * @author Stanislav Muhametsin
 */
public interface Predicate
    extends BooleanExpression
{
    /**
     * A class representing empty predicate. The result of empty predicate is empty string. If empty predicate is
     * encountered inside {@link Conjunction} or {@link Disjunction}, their operator is omitted. So, empty
     * predicate {@code AND} something becomes just something.
     * 
     * @author Stanislav Muhametsin
     */
    public static final class EmptyPredicate
        implements Predicate
    {
        private EmptyPredicate()
        {
        }

        /**
         * Returns {@link EmptyPredicate}.
         */
        public Class getImplementedType()
        {
            return EmptyPredicate.class;
        }

        /**
         * Singleton instance of {@link EmptyPredicate}.
         */
        public static final EmptyPredicate INSTANCE = new EmptyPredicate();
    }
}