1 /*
2 * Copyright 1999-2001,2004 The Apache Software Foundation.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package org.apache.commons.workflow;
18
19
20 /**
21 * <p>A <strong>Block</strong> is a Step that can include nested Steps.
22 * It is used to create Step implementations supporting conditional
23 * execution and iteration.</p>
24 *
25 * <p><strong>DESIGN NOTES</strong> - The <code>execute()</code> method will
26 * be called when the Block is first encountered in the normal flow of
27 * execution (as with any other Step), and each time the execution of the
28 * nested Steps associated with this Block. The Block implementation is
29 * responsible for satisfying the following contract requirements:</p>
30 * <ul>
31 * <li>Determine whether this is a first-time entry, or a repeated entry
32 * after execution of the nested Steps for this Block:
33 * <ul>
34 * <li>Peek at the top item on the <code>BlockState</code> stack maintained
35 * for us by the current <code>Context</code>.</li>
36 * <li>If the top item exists, and has a <code>block</code> property
37 * equal to the current Block, this is a repeated entry after execution
38 * of the nested Steps for this Block.</li>
39 * <li>If there is no top element, or the top element is for a different
40 * <code>Block</code>, this is the initial entry from the preceeding
41 * Step in the current Activity (or Block).</li>
42 * </ul>
43 * <li>When this is the initial entry into the Block, make a decision about
44 * whether the nested Steps should be executed:
45 * <ul>
46 * <li>If the nested Steps <strong>SHOULD</strong> be executed, create a
47 * new <code>BlockState</code> object (associated with this
48 * <code>Block</code>) and push it onto the <code>BlockState</code>
49 * stack. Then, set the next Step to be the first nested Step
50 * for this Block.</li>
51 * <li>If the nested Steps <strong>SHOULD NOT</strong> be executed,
52 * simply return. The next Step will have already been set to the
53 * next Step of the current Activity (or Block) at the same nesting
54 * level.</li>
55 * </ul></li>
56 * <li>When this is a repeated entry into the Block, make a decision about
57 * whether the nested Steps should be executed again:
58 * <ul>
59 * <li>If the nested Steps <strong>SHOULD</strong> be executed again,
60 * set the next Step to be the first nested Step for this Block.</li>
61 * <li>If the nested Steps <strong>SHOULD NOT</strong> be executed again,
62 * pop our <code>BlockState</code> object off of the stack
63 * maintained by our <code>Context</code>. Then, set the next Step
64 * to the <code>nextStep</code> property of this Block, which will
65 * cause execution to flow past the Block.</li>
66 * </ul>
67 * </ul>
68 *
69 * @version $Revision: 155475 $ $Date: 2005-02-26 13:31:11 +0000 (Sat, 26 Feb 2005) $
70 * @author Craig R. McClanahan
71 */
72
73 public interface Block extends Owner, Step {
74
75
76 // --------------------------------------------------------- Public Methods
77
78
79 }