What is ART(Android Run Time), is their any change

Question

I am heard that now Google start using ART, a new run-time for executing Android app and its come with Android 4.4 (in some devices). Now I am just want to confirm that, is pro-grammatically any changes are required or not in existing application or their is any criteria for making new application i.e. run on Dalvik but also compatible with ART ?

Answer 1

I am heard that now Google start using ART, a new run-time for executing Android app and its come with Android 4.4 (in some devices)

ART is not enabled by default on Android 4.4. It is enabled by default on the "L" Developer Preview. It probably will be enabled by default on whatever the next production release of Android is.

is pro-grammatically any changes are required or not in existing application or their is any criteria for making new application i.e. run on Dalvik but also compatible with ART ?

Quoting the documentation (emphasis added):

This document lets you know about things to watch for when migrating an existing app to be compatible with ART. Most apps should just work when running with ART. However, some techniques that work on Dalvik do not work on ART. This document discusses some of these issues.

If you are using the NDK, there's a chance you will need to make some ART-related adjustments. After that, the scenarios in which you would have to change for ART get fairly esoteric.