1 import java.util.ArrayList;
 2 import java.util.Arrays;
 3 import java.util.Collection;
 4 
 5 import org.apache.commons.collections.CollectionUtils;
 6 
 7 public class CollectionModificationHelper<T> {
 8     private Collection<T> oldCollection;
 9     private Collection<T> newCollection;
10     
11     private Collection<T> newElements = new ArrayList<T>();
12     private Collection<T> commonElements = new ArrayList<T>();
13     private Collection<T> removedElements = new ArrayList<T>();
14     
15     public CollectionModificationHelper(Collection<T> oldCollection,
16             Collection<T> newCollection) {
17         super();
18         this.oldCollection = oldCollection;
19         this.newCollection = newCollection;
20         
21         init();
22     }
23     
24     public CollectionModificationHelper(T[] oldArray, T[] newArray) {
25         this((oldArray ==  null ? null : Arrays.asList(oldArray)), (newArray == null ? null : Arrays.asList(newArray)));
26     }
27 
28     private void init() {
29         if(CollectionUtils.isEmpty(oldCollection) && CollectionUtils.isEmpty(newCollection)) {
30             //nothing to do!
31         } else if(CollectionUtils.isEmpty(oldCollection)) {
32             if(!CollectionUtils.isEmpty(newCollection)) {
33                 this.newElements = new ArrayList<T>(newCollection);
34             }
35         } else if(CollectionUtils.isEmpty(newCollection)) {
36             if(!CollectionUtils.isEmpty(oldCollection)) {
37                 this.removedElements = new ArrayList<T>(oldCollection);
38             }
39         } else { 
40             for(T item : oldCollection) {
41                 if(newCollection.contains(item)) {
42                     commonElements.add(item);
43                 } else {
44                     removedElements.add(item);
45                 }
46             }
47             
48             newElements.addAll(newCollection); //first add all new Collection in new element. 
49             newElements.removeAll(commonElements); //then remove the common elements.
50         }
51     }
52 
53     public Collection<T> getCommonElements() {
54         return commonElements;
55     }
56 
57     public Collection<T> getNewElements() {
58         return newElements;
59     }
60 
61     public Collection<T> getRemovedElements() {
62         return removedElements;
63     }
64 }
65