1 /* 2 * Copyright (C) 2015 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.messaging.util; 18 19 /** 20 * Very simple circular array implementation. 21 * 22 * @param <E> The element type of this list. 23 * @LibraryInternal 24 */ 25 public class CircularArray<E> { 26 private int mNextWriter; 27 private boolean mHasWrapped; 28 private int mMaxCount; 29 Object mList[]; 30 31 /** 32 * Constructor for CircularArray. 33 * 34 * @param count Max elements to hold in the list. 35 */ CircularArray(int count)36 public CircularArray(int count) { 37 mMaxCount = count; 38 clear(); 39 } 40 41 /** 42 * Reset the list. 43 */ clear()44 public void clear() { 45 mNextWriter = 0; 46 mHasWrapped = false; 47 mList = new Object[mMaxCount]; 48 } 49 50 /** 51 * Add an element to the end of the list. 52 * 53 * @param object The object to add. 54 */ add(E object)55 public void add(E object) { 56 mList[mNextWriter] = object; 57 ++mNextWriter; 58 if (mNextWriter == mMaxCount) { 59 mNextWriter = 0; 60 mHasWrapped = true; 61 } 62 } 63 64 /** 65 * Get the number of elements in the list. This will be 0 <= returned count <= max count 66 * 67 * @return Elements in the circular list. 68 */ count()69 public int count() { 70 if (mHasWrapped) { 71 return mMaxCount; 72 } else { 73 return mNextWriter; 74 } 75 } 76 77 /** 78 * Return null if the list hasn't wrapped yet. Otherwise return the next object that would be 79 * overwritten. Can be useful to avoid extra allocations. 80 * 81 * @return 82 */ 83 @SuppressWarnings("unchecked") getFree()84 public E getFree() { 85 if (!mHasWrapped) { 86 return null; 87 } else { 88 return (E) mList[mNextWriter]; 89 } 90 } 91 92 /** 93 * Get the object at index. Index 0 is the oldest item inserted into the list. Index (count() - 94 * 1) is the newest. 95 * 96 * @param index Index to retrieve. 97 * @return Object at index. 98 */ 99 @SuppressWarnings("unchecked") get(int index)100 public E get(int index) { 101 if (mHasWrapped) { 102 int wrappedIndex = index + mNextWriter; 103 if (wrappedIndex >= mMaxCount) { 104 wrappedIndex -= mMaxCount; 105 } 106 return (E) mList[wrappedIndex]; 107 } else { 108 return (E) mList[index]; 109 } 110 } 111 } 112