org.apache.hadoop.fs.shell.find.Expression Maven / Gradle / Ivy
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* 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 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 args);
}