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 }