1/* 2 * Copyright (C) 2012 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not 5 * use this file except in compliance with the License. You may obtain a copy of 6 * 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, WITHOUT 12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the 13 * License for the specific language governing permissions and limitations under 14 * the License. 15 */ 16 17package com.android.inputmethod.research; 18 19import com.android.inputmethod.latin.CollectionUtils; 20 21import java.util.LinkedList; 22 23/** 24 * A buffer that holds a fixed number of LogUnits. 25 * 26 * LogUnits are added in and shifted out in temporal order. Only a subset of the LogUnits are 27 * actual words; the other LogUnits do not count toward the word limit. Once the buffer reaches 28 * capacity, adding another LogUnit that is a word evicts the oldest LogUnits out one at a time to 29 * stay under the capacity limit. 30 */ 31public class LogBuffer { 32 protected final LinkedList<LogUnit> mLogUnits; 33 /* package for test */ int mWordCapacity; 34 // The number of members of mLogUnits that are actual words. 35 protected int mNumActualWords; 36 37 /** 38 * Create a new LogBuffer that can hold a fixed number of LogUnits that are words (and 39 * unlimited number of non-word LogUnits), and that outputs its result to a researchLog. 40 * 41 * @param wordCapacity maximum number of words 42 */ 43 LogBuffer(final int wordCapacity) { 44 if (wordCapacity <= 0) { 45 throw new IllegalArgumentException("wordCapacity must be 1 or greater."); 46 } 47 mLogUnits = CollectionUtils.newLinkedList(); 48 mWordCapacity = wordCapacity; 49 mNumActualWords = 0; 50 } 51 52 /** 53 * Adds a new LogUnit to the front of the LIFO queue, evicting existing LogUnit's 54 * (oldest first) if word capacity is reached. 55 */ 56 public void shiftIn(LogUnit newLogUnit) { 57 if (newLogUnit.getWord() == null) { 58 // This LogUnit isn't a word, so it doesn't count toward the word-limit. 59 mLogUnits.add(newLogUnit); 60 return; 61 } 62 if (mNumActualWords == mWordCapacity) { 63 shiftOutThroughFirstWord(); 64 } 65 mLogUnits.add(newLogUnit); 66 mNumActualWords++; // Must be a word, or we wouldn't be here. 67 } 68 69 private void shiftOutThroughFirstWord() { 70 while (!mLogUnits.isEmpty()) { 71 final LogUnit logUnit = mLogUnits.removeFirst(); 72 onShiftOut(logUnit); 73 if (logUnit.hasWord()) { 74 // Successfully shifted out a word-containing LogUnit and made space for the new 75 // LogUnit. 76 mNumActualWords--; 77 break; 78 } 79 } 80 } 81 82 /** 83 * Removes all LogUnits from the buffer without calling onShiftOut(). 84 */ 85 public void clear() { 86 mLogUnits.clear(); 87 mNumActualWords = 0; 88 } 89 90 /** 91 * Called when a LogUnit is removed from the LogBuffer as a result of a shiftIn. LogUnits are 92 * removed in the order entered. This method is not called when shiftOut is called directly. 93 * 94 * Base class does nothing; subclasses may override. 95 */ 96 protected void onShiftOut(LogUnit logUnit) { 97 } 98 99 /** 100 * Called to deliberately remove the oldest LogUnit. Usually called when draining the 101 * LogBuffer. 102 */ 103 public LogUnit shiftOut() { 104 if (mLogUnits.isEmpty()) { 105 return null; 106 } 107 final LogUnit logUnit = mLogUnits.removeFirst(); 108 if (logUnit.hasWord()) { 109 mNumActualWords--; 110 } 111 return logUnit; 112 } 113} 114