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A packaging of the IntelliJ Community Edition java-analysis-impl library. This is release number 1 of trunk branch 142.
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/*
 * Copyright 2011-2014 Bas Leijdekkers
 *
 * 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.siyeh.ig.ui;

import com.intellij.openapi.util.InvalidDataException;
import com.intellij.openapi.util.JDOMExternalizable;
import com.intellij.openapi.util.WriteExternalException;
import com.intellij.openapi.util.text.StringUtil;
import com.intellij.util.ArrayUtil;
import com.intellij.util.containers.OrderedSet;
import org.jdom.Element;
import org.jetbrains.annotations.NonNls;

import java.util.List;

/**
 * Always assign instances of this class to a final field to prevent an InstantiationException
 * from DefaultJDOMExternalizer.
 * 
 * The constructor of this class takes parameters. This means an instance of this class
 * cannot be constructed by {@link com.intellij.openapi.util.DefaultJDOMExternalizer}.
 * If instances of this class are assigned to a final field, DefaultJDOMExternalizer will
 * omit the construction of a new instance and prevent the problem.
 */
@SuppressWarnings({"HardCodedStringLiteral"})
public class ExternalizableStringSet extends OrderedSet
  implements JDOMExternalizable {

  private static final String ITEM = "item";
  private static final String VALUE = "value";

  private final String[] defaultValues;

  /**
   * note: declare ExternalizableStringSet fields as final!

   * note: reference to defaultValues is retained by this set!
   */
  public ExternalizableStringSet(@NonNls String... defaultValues) {
    this.defaultValues = defaultValues.length == 0 ? ArrayUtil.EMPTY_STRING_ARRAY : defaultValues;
    for (String defaultValue : defaultValues) {
      add(defaultValue);
    }
  }

  /*
  private ExternalizableStringSet() {
      throw new AssertionError("ExternalizableStringSet fields should be declared final");
    }
    */

  public boolean hasDefaultValues() {
    if (size() != defaultValues.length) {
      return false;
    }
    for (String defaultValue : defaultValues) {
      if (!contains(defaultValue)) {
        return false;
      }
    }
    return true;
  }

  @Override
  public void readExternal(Element element) throws InvalidDataException {
    boolean dataFound = false;
    for (Element item : (List)element.getChildren(ITEM)) {
      if (!dataFound) {
        clear();
        dataFound = true;
      }
      add(StringUtil.unescapeXml(item.getAttributeValue(VALUE)));
    }
  }

  @Override
  public void writeExternal(Element element) throws WriteExternalException {
    if (hasDefaultValues()) {
      return;
    }
    for (String value : this) {
      if (value != null) {
        final Element item = new Element(ITEM);
        item.setAttribute(VALUE, StringUtil.escapeXml(value));
        element.addContent(item);
      }
    }
  }
}