package org.apache.lucene.store;/** * Copyright 2004 The Apache Software Foundation * * 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. */import java.io.IOException;/** A Directory is a flat list of files.  Files may be written once, when they * are created.  Once a file is created it may only be opened for read, or * deleted.  Random access is permitted both when reading and writing. * * <p> Java's i/o APIs not used directly, but rather all i/o is * through this API.  This permits things such as: <ul> * <li> implementation of RAM-based indices; * <li> implementation indices stored in a database, via JDBC; * <li> implementation of an index as a single file; * </ul> * * @author Doug Cutting */public abstract class Directory {  /** Returns an array of strings, one for each file in the directory. */  public abstract String[] list()       throws IOException;  /** Returns true iff a file with the given name exists. */  public abstract boolean fileExists(String name)       throws IOException;  /** Returns the time the named file was last modified. */  public abstract long fileModified(String name)       throws IOException;  /** Set the modified time of an existing file to now. */  public abstract void touchFile(String name)       throws IOException;  /** Removes an existing file in the directory. */  public abstract void deleteFile(String name)       throws IOException;  /** Renames an existing file in the directory.    If a file already exists with the new name, then it is replaced.    This replacement should be atomic. */  public abstract void renameFile(String from, String to)       throws IOException;  /** Returns the length of a file in the directory. */  public abstract long fileLength(String name)       throws IOException;  /** Creates a new, empty file in the directory with the given name.      Returns a stream writing this file. */  public abstract IndexOutput createOutput(String name) throws IOException;  /** Returns a stream reading an existing file. */  public abstract IndexInput openInput(String name)    throws IOException;  /** Construct a {@link Lock}.   * @param name the name of the lock file   */  public abstract Lock makeLock(String name);  /** Closes the store. */  public abstract void close()       throws IOException;}