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