1、Dalvik VM获取生成的java类文件，将他们组成一个或多个Dalvik可执行文件（.dex），他重用多个类文件的重复信息，相比没有压缩的jar文件空间缩小一倍。Delvik还对垃圾收集进行了优化，而写其采用了一种不同的汇编代码生成方法。
2、FreeType库负责字体支持。
3、SQLite是一个独立的开源项目，没有绑定到Android，适用于SQLite的工具也同样适用于Android数据库。
4、大多数应用程序通过Dalvik VM访问SQLite等这些核心库。
5、模拟器不能模拟USB连接、照相机与视频采集、耳机、电池、蓝牙、WIFI、NFC和OpenGL ES2.0。
6、Android UI是新一代UI框架，他的UI是声明性的，具有独立的主题。
7、Android中的所有对话框都是异步的。
8、Android支持补间动画(Tweening)和逐帧动画。
9、Android中重要的包：
android.app: Implements the Application model for Android. Primary
classes include Application, representing the start and stop
semantics, as well as a number of activity-related classes, fragments,
controls, dialogs, alerts, and notifications.
android.bluetooth: Provides a number of classes to work with
Bluetooth functionality. The main classes include BluetoothAdapter,
BluetoothDevice, BluetoothSocket, BluetoothServerSocket, and
BluetoothClass. You can use BluetoothAdapter to control the locally
installed Bluetooth adapter. For example, you can enable it, disable it,
and start the discovery process. The BluetoothDevice represents the
remote Bluetooth device that you are connecting with. The two
Bluetooth sockets are used to establish communication between the
devices. A Bluetooth class represents the type of Bluetooth device you
are connecting to.
android.content: Implements the concepts of content providers.
Content providers abstract out data access from data stores. This
package also implements the central ideas around intents and Android
Uniform Resource Identifiers (URIs).
android.content.pm: Implements Package Manager-related classes. A
package manager knows about permissions, installed packages,
installed providers, installed services, installed components such as
activities, and installed applications.
android.content.res: Provides access to resource files both
structured and unstructured. The primary classes are AssetManager
(for unstructured resources) and Resources.
android.database: Implements the idea of an abstract database. The
primary interface is the Cursor interface.
android.database.sqlite: Implements the concepts from the
android.database package using SQLite as the physical database.
Primary classes are SQLiteCursor, SQLiteDatabase, SQLiteQuery,
SQLiteQueryBuilder, and SQLiteStatement. However, most of your
interaction is going to be with classes from the abstract
android.database package.
android.gesture: This package houses all the classes and interfaces
necessary to work with user-defined gestures. Primary classes are
Gesture, GestureLibrary, GestureOverlayView, GestureStore,
GestureStroke, GesturePoint. A Gesture is a collection of
GestureStrokes and GesturePoints. Gestures are collected in a
GestureLibrary. Gesture libraries are stored in a GestureStore.
Gestures are named so that they can be identified as actions.
android.graphics: Contains the classes Bitmap, Canvas, Camera, Color,
Matrix, Movie, Paint, Path, Rasterizer, Shader, SweepGradient, and
TypeFace.
android.graphics.drawable: Implements drawing protocols and
background p_w_picpaths, and allows animation of drawable objects.
android.graphics.drawable.shapes: Implements shapes including
ArcShape, OvalShape, PathShape, RectShape, and RoundRectShape.
android.hardware: Implements the physical Camera-related classes.
The Camera represents the hardware camera, whereas
android.graphics.Camera represents a graphical concept that’s not
related to a physical camera at all.
android.location: Contains the classes Address, GeoCoder, Location,
LocationManager, and LocationProvider. The Address class represents
the simplified XAL (Extensible Address Language). GeoCoder allows
you to get a latitude/longitude coordinate given an address, and vice
versa. Location represents the latitude/longitude.
android.media: Contains the classes MediaPlayer, MediaRecorder,
Ringtone, AudioManager, and FaceDetector. MediaPlayer, which
supports streaming, is used to play audio and video. MediaRecorder is
used to record audio and video. The Ringtone class is used to play
short sound snippets that could serve as ringtones and notifications.
AudioManager is responsible for volume controls. You can use
FaceDetector to detect people’s faces in a bitmap.
android.net: Implements the basic socket-level network APIs. Primary
classes include Uri, ConnectivityManager, LocalSocket, and
LocalServerSocket. It is also worth noting here that Android supports
HTTPS at the browser level and also at the network level. Android also
supports JavaScript in its browser.
android.net.wifi: Manages WiFi connectivity. Primary classes include
WifiManager and WifiConfiguration. WifiManager is responsible for
listing the configured networks and the currently active WiFi network.
android.opengl: Contains utility classes surrounding OpenGL ES 1.0
and 2.0 operations. The primary classes of OpenGL ES are
implemented in a different set of packages borrowed from JSR 239.
These packages are javax.microedition.khronos.opengles,
javax.microedition.khronos.egl, and
javax.microedition.khronos.nio. These packages are thin wrappers
around the Khronos implementation of OpenGL ES in C and C++.
android.os: Represents the OS services accessible through the Java
programming language. Some important classes include
BatteryManager, Binder, FileObserver, Handler, Looper, and
PowerManager. Binder is a class that allows interprocess
communication. FileObserver keeps tabs on changes to files. You use
Handler classes to run tasks on the message thread, and Looper to run
a message thread.
android.preference: Allows applications the ability to have users
manage their preferences for that application in a uniform way. The
primary classes are PreferenceActivity, PreferenceScreen, and
various Preference-derived classes such as CheckBoxPreference and
SharedPreferences.
android.provider: Comprises a set of prebuilt content providers
adhering to the android.content.ContentProvider interface. The
content providers include Contacts, MediaStore, Browser, and
Settings. This set of interfaces and classes stores the metadata for
the underlying data structures.
android.sax: Contains an efficient set of Simple API for XML (SAX)
parsing utility classes. Primary classes include Element, RootElement,
and a number of ElementListener interfaces.
android.speech: Contains constants for use with speech recognition.
android.speech.tts: Provides support for converting text to speech.
The primary class is TextToSpeech. You will be able to take text and
ask an instance of this class to queue the text to be spoken. You have
access to a number of callbacks to monitor when the speech has
finished, for example. Android uses the Pico TTS (Text to Speech)
engine from SVOX.
android.telephony: Contains the classes CellLocation,
PhoneNumberUtils, and TelephonyManager. A TelephonyManager lets
you determine cell location, phone number, network operator name,
network type, phone type, and Subscriber Identity Module (SIM) serial
number.
android.telephony.gsm: Allows you to gather cell location based on
cell towers and also hosts classes responsible for SMS messaging.
This package is called GSM because Global System for Mobile
Communication is the technology that originally defined the SMS datamessaging
standard.
android.telephony.cdma: Provides support for CDMA telephony.
android.text: Contains text-processing classes.
android.text.method: Provides classes for entering text input for a
variety of controls.
android.text.style: Provides a number of styling mechanisms for a
span of text.
android.utils: Contains the classes Log, DebugUtils, TimeUtils, and
Xml.
android.view: Contains the classes Menu, View, ViewGroup, and a
series of listeners and callbacks.
android.view.animation: Provides support for tweening animation.
The main classes include Animation, a series of interpolators for
animation, and a set of specific animator classes that include
AlphaAnimation, ScaleAnimation, TranslationAnimation, and
RotationAnimation. Android 3.0 introduced the android.animation
package, which is similar, but more broad because it can work with
objects rather than just views.
android.view.inputmethod: Implements the input-method framework
architecture.
android.webkit: Contains classes representing the web browser. The
primary classes include WebView, CacheManager, and CookieManager.
android.widget: Contains all of the UI controls usually derived from
the View class. Primary widgets include Button, Checkbox,
Chronometer, AnalogClock, DatePicker, DigitalClock, EditText,
ListView, FrameLayout, GridView, ImageButton, MediaController,
ProgressBar, RadioButton, RadioGroup, RatingButton, Scroller,
ScrollView, Spinner, TabWidget, TextView, TimePicker, VideoView, and
ZoomButton.
com.google.android.maps: Contains the classes MapView,
MapController, and MapActivity, essentially classes required to work
with Google maps.