Android First Learn

1.1g-4g
1G Cellular Voice Call
2G PHS using GSM, a military standard in the United States, was later civilian. can send text messages, the Internet URL is not www, is wap.baidu.com
3G can access the Internet, directly with the WWW can be accessed 7.2M
4G LTE 100m/s
5G Huawei 600 million dollars, 10g/s small companies sell products, large companies sell copyright.

2.Android Introduction

• Android was originally developed by Andy Rubin and others, the first mobile phone with Android operating system is T-mobile G1 (HTC)
• The logo of Android is the inspiration for designers to find toilets.
• Android System version Evolution history

1.5 Cupcake (Cupcake)
1.6 Donut (Donut)
2.1 Eclair (Lightning puffs)
2.2 Froyo (Frozen Yogurt)
2.3 Gingerbread (ginger cake)
3.0 Honeycomb (Honeycomb)
4.0 Ice cream SandWich (ice cream sandwich)
4.1 Jelly bean (Jelly Bean)
4.2 Jelly Bean (Jelly Bean)
5.0 Lime Pie (lime pie)
6.0 Marshmallow (Cotton candy)
7.0 Nougat (nougat)

3.Android System Configuration (four-tier architecture)
"1" Linux layer
"2" function library layer
"3" Application framework application frame layer
"4" Top Application layer

The difference between a 4.Dalvic VM and a JVM

• JVM converts Java source code to bytecode
• The DVM Android app is also written in Java, Google has done a Java virtual machine, due to copyright.

• Google Engineering died to turn all the. class files into a. dex file, so that the speed was increased and there was a schema-based difference. The traditional Android program runs under the DVM.

• ART (Android Runtime) mode, before Android 4.4, Android applications are running on a DVM, and this mode relies on a compiler to communicate with the application. Every time the application runs, you need to change the code within the program to run, virtually increased the move to the formalities, resulting in a relatively fast, high memory, even if the flagship machine will be card for a long time.
• Google engineers in fact, in order to work with iOS Pk,art mode through the installation of the application, the program is automatically compiled by the mother pre-read, so that the program directly compiled into machine language, eliminating the Dalvic mode to convert code at all times, to achieve efficiency, power saving, occupy lower system memory, mobile phone running smoothly.
• However, the pros and cons are: it will take up slightly higher storage space, the installer will be compared to the normal Dalvik mode longer time to achieve precompilation.

Android First Learn