package org.apache.lucene.store;

/**
 * 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.
 */

import java.io.File;

/**
 * Base class for file system based locking implementation.
 */

public abstract class FSLockFactory extends LockFactory {

  /**
   * Directory for the lock files.
   */
  protected File lockDir = null;

  /**
   * Set the lock directory. This method can be only called
   * once to initialize the lock directory. It is used by {@link FSDirectory}
   * to set the lock directory to itsself.
   * Subclasses can also use this method to set the directory
   * in the constructor.
   */
  protected void setLockDir(File lockDir) {
    if (this.lockDir != null)
      throw new IllegalStateException("You can set the lock directory for this factory only once.");
    this.lockDir = lockDir;
  }
  
  /**
   * Retrieve the lock directory.
   */
  public File getLockDir() {
    return lockDir;
  }

}

package org.apache.lucene.store;

/**
 * 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.
 */

import java.io.File;

/**
 * Base class for file system based locking implementation.
 */

public abstract class FSLockFactory extends LockFactory {

  /**
   * Directory for the lock files.
   */
  protected File lockDir = null;

  /**
   * Set the lock directory. This method can be only called
   * once to initialize the lock directory. It is used by {@link FSDirectory}
   * to set the lock directory to itsself.
   * Subclasses can also use this method to set the directory
   * in the constructor.
   */
  protected final void setLockDir(File lockDir) {
    if (this.lockDir != null)
      throw new IllegalStateException("You can set the lock directory for this factory only once.");
    this.lockDir = lockDir;
  }
  
  /**
   * Retrieve the lock directory.
   */
  public File getLockDir() {
    return lockDir;
  }

}

make FSLockFactory.setLockDir() final to prevent users from doing bad things. This method was package private before, so no bw-problem, but as it is protected now (because an user's customized FSLockFactory must be able to call it from ctor), it must be final (contract: all methods called from ctors should be private or final).