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This module contains the Table/SQL API for writing table programs within the table ecosystem using the Java programming language.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.flink.table.expressions;

import org.apache.flink.annotation.Internal;

/** A visitor for all {@link Expression}s that might be created during API translation. */
@Internal
public abstract class ApiExpressionVisitor implements ExpressionVisitor {

    public final R visit(Expression other) {
        if (other instanceof UnresolvedReferenceExpression) {
            return visit((UnresolvedReferenceExpression) other);
        } else if (other instanceof TableReferenceExpression) {
            return visit((TableReferenceExpression) other);
        } else if (other instanceof LocalReferenceExpression) {
            return visit((LocalReferenceExpression) other);
        } else if (other instanceof LookupCallExpression) {
            return visit((LookupCallExpression) other);
        } else if (other instanceof UnresolvedCallExpression) {
            return visit((UnresolvedCallExpression) other);
        } else if (other instanceof SqlCallExpression) {
            return visit((SqlCallExpression) other);
        } else if (other instanceof ResolvedExpression) {
            return visit((ResolvedExpression) other);
        }
        return visitNonApiExpression(other);
    }

    // --------------------------------------------------------------------------------------------
    // resolved API expressions
    // --------------------------------------------------------------------------------------------

    public abstract R visit(TableReferenceExpression tableReference);

    public abstract R visit(LocalReferenceExpression localReference);

    /** For resolved expressions created by the planner. */
    public abstract R visit(ResolvedExpression other);

    // --------------------------------------------------------------------------------------------
    // unresolved API expressions
    // --------------------------------------------------------------------------------------------

    public abstract R visit(UnresolvedReferenceExpression unresolvedReference);

    public abstract R visit(LookupCallExpression lookupCall);

    public abstract R visit(UnresolvedCallExpression unresolvedCallExpression);

    public abstract R visit(SqlCallExpression sqlCall);

    // --------------------------------------------------------------------------------------------
    // other expressions
    // --------------------------------------------------------------------------------------------

    public abstract R visitNonApiExpression(Expression other);
}