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      1 /*
      2  * Copyright (C) 2014 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 android.hardware.camera2.utils;
     18 
     19 import java.util.List;
     20 
     21 /**
     22  * Various assortment of list utilities.
     23  *
     24  * <p>Using a {@code null} list is supported and will almost always return the default value
     25  * (e.g. {@code false}, or {@code null}).</p>
     26  */
     27 public class ListUtils {
     28 
     29     /** Return {@code} true if the {@code list} contains the {@code needle}. */
     30     public static <T> boolean listContains(List<T> list, T needle) {
     31         if (list == null) {
     32             return false;
     33         } else {
     34             return list.contains(needle);
     35         }
     36     }
     37 
     38     /**
     39      * Return {@code true} if the {@code list} is only a single element equal to
     40      * {@code single}.
     41      */
     42     public static <T> boolean listElementsEqualTo(List<T> list, T single) {
     43         if (list == null) {
     44             return false;
     45         }
     46 
     47         return (list.size() == 1 && list.contains(single));
     48     }
     49 
     50     /**
     51      * Return a human-readable representation of a list (non-recursively).
     52      */
     53     public static <T> String listToString(List<T> list) {
     54         if (list == null) {
     55             return null;
     56         }
     57 
     58         StringBuilder sb = new StringBuilder();
     59         sb.append('[');
     60 
     61         int size = list.size();
     62         int i = 0;
     63         for (T elem : list) {
     64             sb.append(elem);
     65 
     66             if (i != size - 1) {
     67                 sb.append(',');
     68             }
     69             i++;
     70         }
     71         sb.append(']');
     72 
     73         return sb.toString();
     74     }
     75 
     76     /**
     77      * Return the first item from {@code choices} that is contained in the {@code list}.
     78      *
     79      * <p>Choices with an index closer to 0 get higher priority. If none of the {@code choices}
     80      * are in the {@code list}, then {@code null} is returned.
     81      *
     82      * @param list a list of objects which may or may not contain one or more of the choices
     83      * @param choices an array of objects which should be used to select an item from
     84      *
     85      * @return the first item from {@code choices} contained in {@code list}, otherwise {@code null}
     86      */
     87     public static <T> T listSelectFirstFrom(List<T> list, T[] choices) {
     88         if (list == null) {
     89             return null;
     90         }
     91 
     92         for (T choice : choices) {
     93             if (list.contains(choice)) {
     94                 return choice;
     95             }
     96         }
     97 
     98         return null;
     99     }
    100 
    101     private ListUtils() {
    102         throw new AssertionError();
    103     }
    104 }
    105