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 android.os;
18 
19 import java.util.HashMap;
20 
21 /**
22  * Helper class for writing pooled strings into a Parcel.  It must be used
23  * in conjunction with {@link android.os.PooledStringReader}.  This really needs
24  * to be pushed in to Parcel itself, but doing that is...  complicated.
25  * @hide
26  */
27 public class PooledStringWriter {
28     private final Parcel mOut;
29 
30     /**
31      * Book-keeping for writing pooled string objects, mapping strings we have
32      * written so far to their index in the pool.  We deliberately use HashMap
33      * here since performance is critical, we expect to be doing lots of adds to
34      * it, and it is only a temporary object so its overall memory footprint is
35      * not a signifciant issue.
36      */
37     private final HashMap<String, Integer> mPool;
38 
39     /**
40      * Book-keeping for writing pooling string objects, indicating where we
41      * started writing the pool, which is where we need to ultimately store
42      * how many strings are in the pool.
43      */
44     private int mStart;
45 
46     /**
47      * Next available index in the pool.
48      */
49     private int mNext;
50 
PooledStringWriter(Parcel out)51     public PooledStringWriter(Parcel out) {
52         mOut = out;
53         mPool = new HashMap<>();
54         mStart = out.dataPosition();
55         out.writeInt(0); // reserve space for final pool size.
56     }
57 
writeString(String str)58     public void writeString(String str) {
59         final Integer cur = mPool.get(str);
60         if (cur != null) {
61             mOut.writeInt(cur);
62         } else {
63             mPool.put(str, mNext);
64             mOut.writeInt(-(mNext+1));
65             mOut.writeString(str);
66             mNext++;
67         }
68     }
69 
getStringCount()70     public int getStringCount() {
71         return mPool.size();
72     }
73 
finish()74     public void finish() {
75         final int pos = mOut.dataPosition();
76         mOut.setDataPosition(mStart);
77         mOut.writeInt(mNext);
78         mOut.setDataPosition(pos);
79     }
80 }
81