Getting to know Android for the first time (2018.4.26)

introduce:

Android is an open source operating system based on Linux

Developed and promoted by Google , the first version was launched in 2008 .

This system was originally developed by " the father of Android " Andy Rubin ( 2003 )

——————————————————————————————————————————————————

Overall structure diagram:

What is the structure of an android application ?

Answer: Android adopts a layered architecture, which is divided into four layers, which are divided into application programs from the top layer to the bottom layer.

sequence layer, application framework layer, system runtime layer and Linux core layer

1. Android application layer

2, the application framework layer

3. System runtime layer

4, Linux kernel layer

——————————————————————————————————————————————

The difference between DVM and JVM :

1. The primary difference

• Dalvik : Register based , compiles and runs faster

• JVM: stack - based , slower to compile and run

2. The difference between bytecodes

• Dalvik : Execute the bytecode in .dex format, which is generated by compressing the .class file ,

file gets smaller

• JVM: executes bytecode in .class format

3. Differences in operating environment　 　

• Dalvik :  An application starts running on a separate virtual machine running on a separate

in progress

• JVM: Only one , that is, all applications run in the same JVM

———————————————————————————————————————————————————

first

Configure the path environment variable

Then

Create and launch an emulator in Eclipse

{

AVDName : virtual device name

Device: Device model

Target:系统SDK的版本

CPU/ABI: 处理器

Keyboard: 是否用硬键盘(不选用软键盘)

Skin: 不同型号皮肤外形不相同

MemoryOtions: 内存选项设置

RAM : 设备的运行内存

VM Heap : 虚拟机堆空间内存

InternalStorage : 设备内部存储空间大小

SDCard : SD卡内存的大小

}

——————————————————————————————————————————————————

DVM指Dalvik的虚拟机。每一个Android应用程序

都在它自己的进程中运行，都拥有一个独立的

Dalvik虚拟机实例。而每一个DVM都是在Linux 中

的一个进程，所以说可以认为是同一个概念。