core/src/main/java/org/apache/calcite/runtime/UnionOperation.java

/*
 * 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.calcite.runtime;

import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.operation.union.UnaryUnionOp;

import java.util.ArrayList;
import java.util.List;

/**
 * Used at run time by the ST_Union function.
 */
public class UnionOperation {

  public List<Geometry> init() {
    return new ArrayList<>();
  }

  public List<Geometry> add(List<Geometry> accumulator, Geometry geometry) {
    accumulator.add(geometry);
    return accumulator;
  }

  public Geometry result(List<Geometry> accumulator) {
    return new UnaryUnionOp(accumulator).union();
  }
}