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Simple persistent scheduler for scheduled tasks, recurring or ad-hoc.

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/*
 * Copyright 2015 jmrozanec
 *
 * 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 com.github.kagkarlsson.shaded.cronutils.model.field.expression;

import java.io.Serializable;

import com.github.kagkarlsson.shaded.cronutils.model.field.expression.visitor.FieldExpressionVisitor;

public abstract class FieldExpression implements Serializable {

	private static final long serialVersionUID = 5138279438874391617L;

	public And and(final FieldExpression exp) {
		return new And().and(this).and(exp);
	}

	/**
	 * Represents FieldExpression as string.
	 *
	 * @return String representation, never null.
	 */
	public abstract String asString();

	/**
	 * Accept a visitor to perform some action on the instance. Current instance is
	 * cloned, so that we ensure immutability. Clone of this instance is returned
	 * after visitor.visit(clone) was invoked.
	 *
	 * @param visitor - FieldExpressionVisitor instance, never null
	 * @return FieldExpression copied instance with visitor action performed.
	 */
	public abstract FieldExpression accept(final FieldExpressionVisitor visitor);

	public static FieldExpression always() {
		return Always.INSTANCE;
	}

	public static FieldExpression questionMark() {
		return QuestionMark.INSTANCE;
	}
}