# PDPushButton.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.pdfbox.pdmodel.interactive.form;

    import java.io.IOException;
    import java.util.Collections;
    import java.util.List;
    import java.util.Set;

    import org.apache.pdfbox.cos.COSDictionary;
    import org.apache.pdfbox.cos.COSName;

    /**
     * A pushbutton is a purely interactive control that responds immediately to user
     * input without retaining a permanent value.
     *
     * @author sug
     */
    public class PDPushButton extends PDButton
    {
        /**
         * @see PDField#PDField(PDAcroForm)
         *
         * @param acroForm The acroform.
         */
        public PDPushButton(PDAcroForm acroForm)
        {
            super(acroForm);
            getCOSObject().setFlag(COSName.FF, FLAG_PUSHBUTTON, true);
        }

        /**
         * Constructor.
         *
         * @param acroForm The form that this field is part of.
         * @param field the PDF object to represent as a field.
         * @param parent the parent node of the node
         */
        PDPushButton(PDAcroForm acroForm, COSDictionary field, PDNonTerminalField parent)
        {
            super(acroForm, field, parent);
        }

        @Override
        public List<String> getExportValues()
        {
            return Collections.emptyList();
        }

        @Override
        public void setExportValues(List<String> values)
        {
            if (values != null && !values.isEmpty())
            {
                throw new IllegalArgumentException("A PDPushButton shall not use the Opt entry in the field dictionary");
            }
        }

        @Override
        public String getValue()
        {
            return "";
        }

        @Override
        public String getDefaultValue()
        {
            return "";
        }

        @Override
        public String getValueAsString()
        {
            return getValue();
        }

        @Override
        public Set<String> getOnValues()
        {
            return Collections.emptySet();
        }

        @Override
        void constructAppearances() throws IOException
        {
            // TODO: add appearance handler to generate/update appearance
        }
    }