Java Reference
In-Depth Information
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SQLite
:Thislibraryprovidesapowerfulandlightweightrelationaldatabaseen-
gine that's available to all apps, and that's also used by Mozilla Firefox and
Apple's iPhone for persistent storage.
•
SSL
:Thislibraryprovidessecuresocketslayer-basedsecurityfornetworkcom-
munication.
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Surface Manager
: This library manages access to the display subsystem, and
seamlessly composites 2D and 3D graphic layers from multiple apps.
Androidprovidesaruntimeenvironmentthatconsistsofcorelibraries(implementing
asubsetoftheApacheHarmonyJava5implementation)andtheDalvikvirtualmachine
(a non-Java virtual machine that's based on processor registers instead of being stack-
based).
Note
Google's Dan Bornstein created Dalvik and named this virtual machine after
an Icelandic fishing village where some of his ancestors lived.
Each Android app defaults to running in its own Linux process, which hosts an in-
stanceofDalvik.Thisvirtualmachine hasbeendesignedsothatdevicescanrunmul-
tiple virtual machines efficiently. This efficiency is largely due to Dalvik executing
DalvikExecutable(DEX)-basedfiles—DEXisaformatthat'soptimizedforaminimal
memory footprint.
Note
Androidstartsaprocesswhenanypartoftheappneedstoexecute,andshuts
downtheprocesswhenit'snolongerneededandenvironmentalresourcesarerequired
by other apps.
Perhaps you're wondering how it's possible to have a non-Java virtual machine run
Javacode.TheansweristhatDalvikdoesn'trunJavacode.Instead,Androidtransforms
compiled Java classfiles into the DEX format, and it's this resulting code that gets ex-
ecuted by Dalvik.
Finally,thelibrariesandAndroidruntimerelyontheLinuxkernel(version2.6.
x
)for
underlyingcoreservices,suchasthreading,low-levelmemorymanagement,anetwork
stack,processmanagement,andadrivermodel.Furthermore,thekernelactsasanab-
straction layer between the hardware and the rest of the software stack.
ANDROID SECURITY MODEL
Android'sarchitectureincludesasecuritymodelthatpreventsappsfromperforming
operations considered harmful to other apps, Linux, or users. This security model,
