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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;
     18 
     19 import android.content.Context;
     20 
     21 import java.util.Iterator;
     22 import java.util.List;
     23 
     24 /**
     25  * Class used for collapsing data items into groups of similar items. The data items that should be
     26  * collapsible should implement the Collapsible interface. The class also contains a utility
     27  * function that takes an ArrayList of items and returns a list of the same items collapsed into
     28  * groups.
     29  */
     30 public final class Collapser {
     31 
     32     /*
     33      * This utility class cannot be instantiated.
     34      */
     35     private Collapser() {}
     36 
     37     /*
     38      * The Collapser uses an n^2 algorithm so we don't want it to run on
     39      * lists beyond a certain size. This specifies the maximum size to collapse.
     40      */
     41     private static final int MAX_LISTSIZE_TO_COLLAPSE = 20;
     42 
     43     /*
     44      * Interface implemented by data types that can be collapsed into groups of similar data. This
     45      * can be used for example to collapse similar contact data items into a single item.
     46      */
     47     public interface Collapsible<T> {
     48         public void collapseWith(T t);
     49         public boolean shouldCollapseWith(T t, Context context);
     50 
     51     }
     52 
     53     /**
     54      * Collapses a list of Collapsible items into a list of collapsed items. Items are collapsed
     55      * if {@link Collapsible#shouldCollapseWith(Object)} returns true, and are collapsed
     56      * through the {@Link Collapsible#collapseWith(Object)} function implemented by the data item.
     57      *
     58      * @param list List of Objects of type <T extends Collapsible<T>> to be collapsed.
     59      */
     60     public static <T extends Collapsible<T>> void collapseList(List<T> list, Context context) {
     61 
     62         int listSize = list.size();
     63         // The algorithm below is n^2 so don't run on long lists
     64         if (listSize > MAX_LISTSIZE_TO_COLLAPSE) {
     65             return;
     66         }
     67 
     68         for (int i = 0; i < listSize; i++) {
     69             T iItem = list.get(i);
     70             if (iItem != null) {
     71                 for (int j = i + 1; j < listSize; j++) {
     72                     T jItem = list.get(j);
     73                     if (jItem != null) {
     74                         if (iItem.shouldCollapseWith(jItem, context)) {
     75                             iItem.collapseWith(jItem);
     76                             list.set(j, null);
     77                         } else if (jItem.shouldCollapseWith(iItem, context)) {
     78                             jItem.collapseWith(iItem);
     79                             list.set(i, null);
     80                             break;
     81                         }
     82                     }
     83                 }
     84             }
     85         }
     86 
     87         // Remove the null items
     88         Iterator<T> itr = list.iterator();
     89         while (itr.hasNext()) {
     90             if (itr.next() == null) {
     91                 itr.remove();
     92             }
     93         }
     94 
     95     }
     96 }
     97