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      1 /*
      2  * Copyright (C) 2009 The Android Open Source Project
      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 com.android.contacts.common;
     18 
     19 import java.util.Iterator;
     20 import java.util.List;
     21 
     22 /**
     23  * Class used for collapsing data items into groups of similar items. The data items that should be
     24  * collapsible should implement the Collapsible interface. The class also contains a utility
     25  * function that takes an ArrayList of items and returns a list of the same items collapsed into
     26  * groups.
     27  */
     28 public final class Collapser {
     29 
     30     /*
     31      * This utility class cannot be instantiated.
     32      */
     33     private Collapser() {}
     34 
     35     /*
     36      * The Collapser uses an n^2 algorithm so we don't want it to run on
     37      * lists beyond a certain size. This specifies the maximum size to collapse.
     38      */
     39     private static final int MAX_LISTSIZE_TO_COLLAPSE = 20;
     40 
     41     /*
     42      * Interface implemented by data types that can be collapsed into groups of similar data. This
     43      * can be used for example to collapse similar contact data items into a single item.
     44      */
     45     public interface Collapsible<T> {
     46         public void collapseWith(T t);
     47         public boolean shouldCollapseWith(T t);
     48     }
     49 
     50     /**
     51      * Collapses a list of Collapsible items into a list of collapsed items. Items are collapsed
     52      * if {@link Collapsible#shouldCollapseWith(Object)} returns true, and are collapsed
     53      * through the {@Link Collapsible#collapseWith(Object)} function implemented by the data item.
     54      *
     55      * @param list List of Objects of type <T extends Collapsible<T>> to be collapsed.
     56      */
     57     public static <T extends Collapsible<T>> void collapseList(List<T> list) {
     58 
     59         int listSize = list.size();
     60         // The algorithm below is n^2 so don't run on long lists
     61         if (listSize > MAX_LISTSIZE_TO_COLLAPSE) {
     62             return;
     63         }
     64 
     65         for (int i = 0; i < listSize; i++) {
     66             T iItem = list.get(i);
     67             if (iItem != null) {
     68                 for (int j = i + 1; j < listSize; j++) {
     69                     T jItem = list.get(j);
     70                     if (jItem != null) {
     71                         if (iItem.shouldCollapseWith(jItem)) {
     72                             iItem.collapseWith(jItem);
     73                             list.set(j, null);
     74                         } else if (jItem.shouldCollapseWith(iItem)) {
     75                             jItem.collapseWith(iItem);
     76                             list.set(i, null);
     77                             break;
     78                         }
     79                     }
     80                 }
     81             }
     82         }
     83 
     84         // Remove the null items
     85         Iterator<T> itr = list.iterator();
     86         while (itr.hasNext()) {
     87             if (itr.next() == null) {
     88                 itr.remove();
     89             }
     90         }
     91 
     92     }
     93 }
     94