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Android High Performance Programming

You're reading from   Android High Performance Programming Build fast and efficient Android apps that run as reliably as clockwork in a multi-device world

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Product type Paperback
Published in Aug 2016
Publisher Packt
ISBN-13 9781785288951
Length 412 pages
Edition 1st Edition
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Authors (2):
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Enrique López Mañas Enrique López Mañas
Author Profile Icon Enrique López Mañas
Enrique López Mañas
Diego Grancini Diego Grancini
Author Profile Icon Diego Grancini
Diego Grancini
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Toc

Table of Contents (12) Chapters Close

Preface 1. Introduction: Why High Performance? FREE CHAPTER 2. Efficient Debugging 3. Building Layouts 4. Memory 5. Multithreading 6. Networking 7. Security 8. Optimizing Battery Consumption 9. Native Coding in Android 10. Performance Tips Index

JNI


JNI stands for Java Native Interface. JNI allows libraries and software written in other languages to access the Java code that is running in the Java Virtual Machine (JVM). This is not something Android-related, but a programming framework that has existed and been used previously in the Java world.

JNI needs files to be declared into either C or C++—it can even connect to Objective-C files. This is what an example in C looks like:

jstring
Java_com_my_package_HelloJni_stringFromJNI( JNIEnv* env,
                                                  jobject thiz )
{
    return (*env)->NewStringUTF(env, "Hello World");
}

Observing the file, we can see that after the return type, jstring, which is equivalent to a string, there is structure with the word Java, the package name, the class name, and the method name. An object, JNIEnv, is always passed as a parameter, as well as jobject—this is required to make the framework interface with Java. The function, written in C, just returns a string...

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