001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.fs.shell.find;
019
020import java.io.IOException;
021import java.util.Deque;
022
023import org.apache.hadoop.fs.shell.PathData;
024
025/**
026 * Interface describing an expression to be used in the
027 * {@link org.apache.hadoop.fs.shell.find.Find} command.
028 */
029public interface Expression {
030  /**
031   * Set the options for this expression, called once before processing any
032   * items.
033   */
034  public void setOptions(FindOptions options) throws IOException;
035
036  /**
037   * Prepares the expression for execution, called once after setting options
038   * and before processing any options.
039   * @throws IOException
040   */
041  public void prepare() throws IOException;
042
043  /**
044   * Apply the expression to the specified item, called once for each item.
045   *
046   * @param item {@link PathData} item to be processed
047   * @param depth distance of the item from the command line argument
048   * @return {@link Result} of applying the expression to the item
049   */
050  public Result apply(PathData item, int depth) throws IOException;
051
052  /**
053   * Finishes the expression, called once after processing all items.
054   *
055   * @throws IOException
056   */
057  public void finish() throws IOException;
058
059  /**
060   * Returns brief usage instructions for this expression. Multiple items should
061   * be returned if there are multiple ways to use this expression.
062   *
063   * @return array of usage instructions
064   */
065  public String[] getUsage();
066
067  /**
068   * Returns a description of the expression for use in help. Multiple lines
069   * should be returned array items. Lines should be formated to 60 characters
070   * or less.
071   *
072   * @return array of description lines
073   */
074  public String[] getHelp();
075
076  /**
077   * Indicates whether this expression performs an action, i.e. provides output
078   * back to the user.
079   */
080  public boolean isAction();
081
082  /** Identifies the expression as an operator rather than a primary. */
083  public boolean isOperator();
084
085  /**
086   * Returns the precedence of this expression
087   * (only applicable to operators).
088   */
089  public int getPrecedence();
090
091  /**
092   * Adds children to this expression. Children are popped from the head of the
093   * deque.
094   *
095   * @param expressions
096   *          deque of expressions from which to take the children
097   */
098  public void addChildren(Deque<Expression> expressions);
099
100  /**
101   * Adds arguments to this expression. Arguments are popped from the head of
102   * the deque and added to the front of the child list, ie last child added is
103   * the first evaluated.
104   * @param args deque of arguments from which to take expression arguments
105   */
106  public void addArguments(Deque<String> args);
107}