001 /*
002 * Copyright 1999-2001,2004 The Apache Software Foundation.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package org.apache.commons.workflow;
018
019
020 /**
021 * <p>A <strong>Block</strong> is a Step that can include nested Steps.
022 * It is used to create Step implementations supporting conditional
023 * execution and iteration.</p>
024 *
025 * <p><strong>DESIGN NOTES</strong> - The <code>execute()</code> method will
026 * be called when the Block is first encountered in the normal flow of
027 * execution (as with any other Step), and each time the execution of the
028 * nested Steps associated with this Block. The Block implementation is
029 * responsible for satisfying the following contract requirements:</p>
030 * <ul>
031 * <li>Determine whether this is a first-time entry, or a repeated entry
032 * after execution of the nested Steps for this Block:
033 * <ul>
034 * <li>Peek at the top item on the <code>BlockState</code> stack maintained
035 * for us by the current <code>Context</code>.</li>
036 * <li>If the top item exists, and has a <code>block</code> property
037 * equal to the current Block, this is a repeated entry after execution
038 * of the nested Steps for this Block.</li>
039 * <li>If there is no top element, or the top element is for a different
040 * <code>Block</code>, this is the initial entry from the preceeding
041 * Step in the current Activity (or Block).</li>
042 * </ul>
043 * <li>When this is the initial entry into the Block, make a decision about
044 * whether the nested Steps should be executed:
045 * <ul>
046 * <li>If the nested Steps <strong>SHOULD</strong> be executed, create a
047 * new <code>BlockState</code> object (associated with this
048 * <code>Block</code>) and push it onto the <code>BlockState</code>
049 * stack. Then, set the next Step to be the first nested Step
050 * for this Block.</li>
051 * <li>If the nested Steps <strong>SHOULD NOT</strong> be executed,
052 * simply return. The next Step will have already been set to the
053 * next Step of the current Activity (or Block) at the same nesting
054 * level.</li>
055 * </ul></li>
056 * <li>When this is a repeated entry into the Block, make a decision about
057 * whether the nested Steps should be executed again:
058 * <ul>
059 * <li>If the nested Steps <strong>SHOULD</strong> be executed again,
060 * set the next Step to be the first nested Step for this Block.</li>
061 * <li>If the nested Steps <strong>SHOULD NOT</strong> be executed again,
062 * pop our <code>BlockState</code> object off of the stack
063 * maintained by our <code>Context</code>. Then, set the next Step
064 * to the <code>nextStep</code> property of this Block, which will
065 * cause execution to flow past the Block.</li>
066 * </ul>
067 * </ul>
068 *
069 * @version $Revision: 155475 $ $Date: 2005-02-26 13:31:11 +0000 (Sat, 26 Feb 2005) $
070 * @author Craig R. McClanahan
071 */
072
073 public interface Block extends Owner, Step {
074
075
076 // --------------------------------------------------------- Public Methods
077
078
079 }