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/*
* Copyright (C) 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.android.messaging.util;
/**
* Very simple circular array implementation.
*
* @param <E> The element type of this list.
* @LibraryInternal
*/
public class CircularArray<E> {
private int mNextWriter;
private boolean mHasWrapped;
private int mMaxCount;
Object mList[];
/**
* Constructor for CircularArray.
*
* @param count Max elements to hold in the list.
*/
public CircularArray(int count) {
mMaxCount = count;
clear();
}
/**
* Reset the list.
*/
public void clear() {
mNextWriter = 0;
mHasWrapped = false;
mList = new Object[mMaxCount];
}
/**
* Add an element to the end of the list.
*
* @param object The object to add.
*/
public void add(E object) {
mList[mNextWriter] = object;
++mNextWriter;
if (mNextWriter == mMaxCount) {
mNextWriter = 0;
mHasWrapped = true;
}
}
/**
* Get the number of elements in the list. This will be 0 <= returned count <= max count
*
* @return Elements in the circular list.
*/
public int count() {
if (mHasWrapped) {
return mMaxCount;
} else {
return mNextWriter;
}
}
/**
* Return null if the list hasn't wrapped yet. Otherwise return the next object that would be
* overwritten. Can be useful to avoid extra allocations.
*
* @return
*/
@SuppressWarnings("unchecked")
public E getFree() {
if (!mHasWrapped) {
return null;
} else {
return (E) mList[mNextWriter];
}
}
/**
* Get the object at index. Index 0 is the oldest item inserted into the list. Index (count() -
* 1) is the newest.
*
* @param index Index to retrieve.
* @return Object at index.
*/
@SuppressWarnings("unchecked")
public E get(int index) {
if (mHasWrapped) {
int wrappedIndex = index + mNextWriter;
if (wrappedIndex >= mMaxCount) {
wrappedIndex -= mMaxCount;
}
return (E) mList[wrappedIndex];
} else {
return (E) mList[index];
}
}
}
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