hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/shell/find/Expression.java

/**
 * 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.
 */
package org.apache.hadoop.fs.shell.find;

import java.io.IOException;
import java.util.Deque;

import org.apache.hadoop.fs.shell.PathData;

/**
 * Interface describing an expression to be used in the
 * {@link org.apache.hadoop.fs.shell.find.Find} command.
 */
public interface Expression {
  /**
   * Set the options for this expression, called once before processing any
   * items.
   */
  public void setOptions(FindOptions options) throws IOException;

  /**
   * Prepares the expression for execution, called once after setting options
   * and before processing any options.
   * @throws IOException
   */
  public void prepare() throws IOException;

  /**
   * Apply the expression to the specified item, called once for each item.
   *
   * @param item {@link PathData} item to be processed
   * @param depth distance of the item from the command line argument
   * @return {@link Result} of applying the expression to the item
   */
  public Result apply(PathData item, int depth) throws IOException;

  /**
   * Finishes the expression, called once after processing all items.
   *
   * @throws IOException
   */
  public void finish() throws IOException;

  /**
   * Returns brief usage instructions for this expression. Multiple items should
   * be returned if there are multiple ways to use this expression.
   *
   * @return array of usage instructions
   */
  public String[] getUsage();

  /**
   * Returns a description of the expression for use in help. Multiple lines
   * should be returned array items. Lines should be formated to 60 characters
   * or less.
   *
   * @return array of description lines
   */
  public String[] getHelp();

  /**
   * Indicates whether this expression performs an action, i.e. provides output
   * back to the user.
   */
  public boolean isAction();

  /** Identifies the expression as an operator rather than a primary. */
  public boolean isOperator();

  /**
   * Returns the precedence of this expression
   * (only applicable to operators).
   */
  public int getPrecedence();

  /**
   * Adds children to this expression. Children are popped from the head of the
   * deque.
   *
   * @param expressions
   *          deque of expressions from which to take the children
   */
  public void addChildren(Deque<Expression> expressions);

  /**
   * Adds arguments to this expression. Arguments are popped from the head of
   * the deque and added to the front of the child list, ie last child added is
   * the first evaluated.
   * @param args deque of arguments from which to take expression arguments
   */
  public void addArguments(Deque<String> args);
}