diff --git a/Contact.java b/Contact.java
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+/*
+ * Copyright (c) 2010-2011, The MiCode Open Source Community (www.micode.net)
+ *
+ * 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 net.micode.notes.data;
+
+import android.content.Context;
+import android.database.Cursor;
+import android.provider.ContactsContract.CommonDataKinds.Phone;
+import android.provider.ContactsContract.Data;
+import android.telephony.PhoneNumberUtils;
+import android.util.Log;
+
+import java.util.HashMap;
+
+/**
+ * <b>联系人查询工具类</b>
+ * <p>
+ * 主要负责根据电话号码从Android数据库中检索联系人姓名。
+ * </p>
+ *
+ * <h3>核心功能：</h3>
+ * <ul>
+ *   <li>基于电话号码查找姓名。</li>
+ *   <li>维护 {@code HashMap} 缓存，减少 IPC 调用次数。</li>
+ *   <li>处理国际化号码格式匹配问题。</li>
+ * </ul>
+ *
+ * @author 林迪文
+ * @version 1.0
+ * @see android.provider.ContactsContract
+ */
+public class Contact {
+    //键值对，用于缓存<姓名,文本>，提高查找速度。
+    private static HashMap<String, String> sContactCache;
+    //fianl意思是常量，TAG为Contact的“别名”。
+    private static final String TAG = "Contact";
+
+    //这是个SQL语句，CALLER_ID_SELECTION是个字符串，作用是构建匹配模式，用and连接了3个部分：电话匹配、数据类型需是电话、号码必须存在于快速查找表中
+    private static final String CALLER_ID_SELECTION = "PHONE_NUMBERS_EQUAL(" + Phone.NUMBER
+    + ",?) AND " + Data.MIMETYPE + "='" + Phone.CONTENT_ITEM_TYPE + "'"
+    + " AND " + Data.RAW_CONTACT_ID + " IN "    //Data哪来的
+            + "(SELECT raw_contact_id "
+            + " FROM phone_lookup"
+            + " WHERE min_match = '+')";
+
+    //主函数，输入电话，根据context，返回人名
+    public static String getContact(Context context, String phoneNumber) {
+        if(sContactCache == null) {
+            sContactCache = new HashMap<String, String>();
+        }   //初次调用getContact时，创建缓存
+
+        if(sContactCache.containsKey(phoneNumber)) {
+            return sContactCache.get(phoneNumber);
+        }   //缓存命中
+
+        String selection = CALLER_ID_SELECTION.replace("+",
+                PhoneNumberUtils.toCallerIDMinMatch(phoneNumber));  //用处理过的电话号码，替代CALLER_ID_SELECTION的+。
+        Cursor cursor = context.getContentResolver().query(
+                Data.CONTENT_URI,   //查找对象
+                new String [] { Phone.DISPLAY_NAME },   //需要返回的是名字这一列
+                selection,  //查找条件
+                new String[] { phoneNumber },   //query可以将phoneNumber填到selection的'？'中
+                null);  //不需排序
+
+        if (cursor != null && cursor.moveToFirst()) {   //cursor.moveToFirst()为true代表至少有一条记录
+            try {
+                String name = cursor.getString(0);
+                sContactCache.put(phoneNumber, name);
+                return name;
+            } catch (IndexOutOfBoundsException e) {     //越界报错
+                Log.e(TAG, " Cursor get string error " + e.toString());
+                return null;
+            } finally {
+                cursor.close(); //关闭进程，防止内存泄露
+            }
+        }
+        else {
+            Log.d(TAG, "No contact matched with number:" + phoneNumber);    //没找到
+            return null;
+        }
+    }
+}