CompoundDiff


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19  
20  package org.apache.cayenne.graph;
21  
22  import java.util.ArrayList  ;
23  import java.util.Collection  ;
24  import java.util.Collections  ;
25  import java.util.Iterator  ;
26  import java.util.List  ;
27  import java.util.ListIterator  ;
28  
29  /**
30   * A GraphDiff that is a list of other GraphDiffs.
31   * 
32   * @since 1.2
33   * @author Andrus Adamchik
34   */
35  public class CompoundDiff implements GraphDiff {
36  
37      protected List   diffs;
38  
39      /**
40       * Creates an empty CompoundDiff instance.
41       */
42      public CompoundDiff() {
43      }
44  
45      /**
46       * Creates CompoundDiff instance. Note that a List is not cloned in this constructor,
47       * so subsequent calls to add and addAll would modify the original list.
48       */
49      public CompoundDiff(List   diffs) {
50          this.diffs = diffs;
51      }
52  
53      /**
54       * Returns true if this diff has no other diffs or if all of its diffs are noops.
55       */
56      public boolean isNoop() {
57          if (diffs == null || diffs.isEmpty()) {
58              return true;
59          }
60  
61          Iterator   it = diffs.iterator();
62          while (it.hasNext()) {
63              if (!((GraphDiff) it.next()).isNoop()) {
64                  return false;
65              }
66          }
67  
68          return true;
69      }
70  
71      public List   getDiffs() {
72          return (diffs != null)
73                  ? Collections.unmodifiableList(diffs)
74                  : Collections.EMPTY_LIST;
75      }
76  
77      public void add(GraphDiff diff) {
78          nonNullDiffs().add(diff);
79      }
80  
81      public void addAll(Collection   diffs) {
82          nonNullDiffs().addAll(diffs);
83      }
84  
85      /**
86       * Iterates over diffs list, calling "apply" on each individual diff.
87       */
88      public void apply(GraphChangeHandler tracker) {
89          if (diffs == null) {
90              return;
91          }
92  
93          // implements a naive linear commit - simply replay stored operations
94          Iterator   it = diffs.iterator();
95          while (it.hasNext()) {
96              GraphDiff change = (GraphDiff) it.next();
97              change.apply(tracker);
98          }
99      }
100 
101     /**
102      * Iterates over diffs list in reverse order, calling "apply" on each individual diff.
103      */
104     public void undo(GraphChangeHandler tracker) {
105         if (diffs == null) {
106             return;
107         }
108 
109         ListIterator   it = diffs.listIterator(diffs.size());
110         while (it.hasPrevious()) {
111             GraphDiff change = (GraphDiff) it.previous();
112             change.undo(tracker);
113         }
114     }
115 
116     List   nonNullDiffs() {
117         if (diffs == null) {
118             synchronized (this) {
119                 if (diffs == null) {
120                     diffs = new ArrayList  ();
121                 }
122             }
123         }
124 
125         return diffs;
126     }
127 }
128
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