platform/indexing-impl/src/com/intellij/util/indexing/ScalarIndexExtension.java

/*
 * Copyright 2000-2014 JetBrains s.r.o.
 *
 * 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.intellij.util.indexing;

import com.intellij.util.io.DataExternalizer;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

/**
 * A specialization of FileBasedIndexExtension allowing to create a mapping [DataObject -> List of files containing this object]
 *
 */
public abstract class ScalarIndexExtension<K> extends FileBasedIndexExtension<K, Void>{

  public static final DataExternalizer<Void> VOID_DATA_EXTERNALIZER = new VoidDataExternalizer();

  @NotNull
  @Override
  public final DataExternalizer<Void> getValueExternalizer() {
    return VOID_DATA_EXTERNALIZER;
  }

  private static class VoidDataExternalizer implements DataExternalizer<Void> {

    @Override
    public void save(@NotNull final DataOutput out, final Void value) throws IOException {
    }

    @Override
    @Nullable
    public Void read(@NotNull final DataInput in) throws IOException {
      return null;
    }
  }
}