Compiling java code on android

Краткое описание:
Работа с java

##О приложении
Этот проект создан для изучения и создания Java приложений на Android.
Вы можете создать и запустить Ява-приложение с JDK 1.7.

(НЕт оффициальной поддержки) Создайте apk-файл (поддержка только armeabi-v7a, x86, x86_64)

## Туториалы(Советы по использованию)
1. Настройте систему https://youtu.be/FZtSbgq8ZN0
2. Создайте файл при помощи библиотеки https://youtu.be/fUFqR8ZlChg
3. Создайте Android приложение https://youtu.be/euZilR8-EhA

##Внимание
Это бета версия,которая будет часто обновляться.

## Todo(. Оставлено по английски,иначе будет утрачен смысл.
1. Java compiler JDK 1.7 ✔
2. Java editor ✔
3. Java auto complete code ✔ (But not working perfect)
4. Java debugger (jdb).
5. Run java file, class file ✔
6. Build java library ✔
7. Support VCS
8. Decompile class, jar
9. Java code formatter (Google Java code formatter) ✔
10. Build Android app. ✔
11. XML auto complete
12. Layout builder for Android

## Что содержит проект?
1. Javac — Java compiler
2. Aapt — Android asset package tool
3. Dx — Dex for dalvik vm
4. Zip Signer
5. Apk сборщик

Это приложение бесплатно, потому что я хочу помочь людям изучать Java. Я работаю для людей. Если вы хотите поддержать проект нажмите на кнопку Донат в приложении.

## Overview
This project is develop to help the community learn java on android.
You can build and run Java file with JDK 1.7.

(No official support) Build apk file (only support armeabi-v7a, x86, x86_64)

##Attention
Because this is beta version so I will update very often.

## Todo
1. Java compiler JDK 1.7 ✔
2. Java editor ✔
3. Java auto complete code ✔ (But not working perfect)
4. Java debugger (jdb).
5. Run java file, class file ✔
6. Build java library ✔
7. Support VCS
8. Decompile class, jar
9. Java code formatter (Google Java code formatter) ✔
10. Build Android app. ✔
11. XML auto complete
12. Layout builder for Android

## What does tools the project include?
1. Javac — Java compiler
2. Aapt — Android asset package tool
3. Dx — Dex for dalvik vm
4. Zip Signer
5. Apk builder

## Contribute
I would absolutely love every possible kind of contributions. If you
have a questions, ideas, need help or want to propose a change just open
an issue. Pull request are greatly appreciated.

This app is free for everyone to learn Java. I work for the community. If you want to donate to the project, you can click donate button in the application.

Источник

Process of compiling Android app with Java/Kotlin code

Jan 28, 2020 · 6 min read

Did you ever wonder what the process of compiling your Java/Kotlin code and running application on Android device look like? What happens under the hood?

Well, the goal of this article is to explain the compilation process of an Android app.

As we all know, Android apps can be written in Java and Kotlin programming languages. So the process of Android app compilation is based on the compilation process of Java and Kotlin code (aside from Android environment). Therefor let’s familiarize ourselves with those two processes.

Java code compilation

In order for J a va code to run, there are couple of steps which need to be done. For demonstration purpose let’s say we have TestClass.java file which we want to run. The steps for compiling the given file will be the following:

TestClass.java is compiled by javac (Java compiler).
Javac compiles Java source file into Java byte-code file as TestClass.class.
Java byte-code file ( TestClass.class) ends up in JVM (Java Virtual Machine).
JVM understands byte-code and converts it into machine code, using JIT (Just-In-Time) compiler.
The machine code is then fed to the memory and executed by computer’s central processing unit.

Generally that is the whole process of running Java code, but I would also like to explain few of the mentioned terms.

Java byte-code — representation of Java assembly.

JVM (Java Virtual Machine)— engine which provides runtime environment for execution of Java code.
JIT (Just-In-Time) compiler— type of compiler which does the compilation during the execution of a program (compiles the app when user opens it).

With that being said, we can conclude topic regarding Java code compilation.

Kotlin code compilation

By definition, Kotlin is a statically-typed open-source programming language generating code that can run on the JVM.

To be able to run on the JVM it needs to compile to Java byte-code. If we check Kotlin’s FAQ, that is exactly what Kotlin compiler does.

What does Kotlin compile down to?

When targeting the JVM, Kotlin produces Java compatible bytecode.

By looking at the left image, we can conclude that the compilation processes of Java and Kotlin are almost the same.

Android compilation process

The main difference between regular Java/Kotlin code compilation and Android compilation process is that Android doesn’t work with JVM (if you wonder why, you can find the answer at the end of the article).

Instead Android decided to create two virtual machines specifically for Android:

DVM (Dalvik Virtual Machine)
ART (Android Runtime) — introduced with the release of Android 4.4 (Kitkat), and before it the runtime environment for Android apps was DVM.

Differences between DVM and ART are described later on in this article.

Regarding their functionalities, ART and Dalvik are compatible runtimes running Dex byte-code which can be found in .dex file.

Now the question arises, from where do we get .dex file?

It turns out, there is one more compiler placed between Java byte-code (.class file) and DVM. Its name is DX (DEX compiler) and its purpose is to convert Java byte-code into Dalvik byte-code.

With that being said, we have all parts for Android compilation process and we can represent it as following

Also it would be interesting to check how Dalvik byte-code looks like. Here is the example of previously mentioned function addTwoNumbers as regular code, its Java byte-code equivalent and its Dalvik byte-code equivalent.

At this point we’ve achieved the main goal of this article, we can say that we found the answers to the questions:

How does Android compilation process look like?
What happens under the hood with Java/Kotlin code?

I really hope that I’ve helped you understand, even a little bit better, Android compilation process.

Still, there are 2 more questions, which I asked myself while learning about compilation process. So as bonus, I would like to familiarize you with them before I finish this article.

Why does Android have two virtual machines?
And why didn’t Google just use JVM?

DVM vs ART

As mentioned before, ART was built as a replacement for DVM. It was introduced in Android 4.4, Kitkat.

The main improvement was that ART uses AOT (Ahead-Of-Time) compilation, while DVM uses JIT (Just-In-Time).

As explained before, JIT compilation does the compilation during the execution of a program (compiles the app on its startup process). This leads to slower startup time of apps, because it needs to compile app every time user opens it.

On other hand AOT compilation does the compilation when the app is installed. By using on-device dex2oat tool, AOT accepts .dex files as input and generates a compiled app executable for the target device. This can lead to much faster and better app performance. As ART compiles app machine code at its installation, there is no need for translation to machine code every time user opens the app, so AOT doesn’t hit the CPU as hard as Just-In-Time code compiling on Dalvik. Less CPU usage results in less battery drain, which is also important benefit for any Android device.

Apart from AOT compilation, ART brought couple of more improvements to the table: Garbage Collection improvements and Debug and Development improvements. If you would like to learn more about them, you can check out the official documentation.

Why didn’t Google use JVM instead of creating another virtual machine?

There are number of reasons why Google has chosen to abandon the JVM. They knew that Android application runtime must support a diverse set of devices with diverse set of resources, and that applications must be sandboxed for security, performance, and reliability reasons. But a virtual machine-based runtime doesn’t enable all that with limited processor speed and RAM.

As solution of mentioned problems, Google has chosen to abandon the JVM in favor of an alternative deployment target, the Dalvik virtual machine (DVM).

DVM vs JVM

By answering to side questions, I can wrap up this article which followed my process of learning regarding Android compilation process.

Thank you for taking time to read my article. I hope it was helpful and please feel free to comment or give me any feedback regarding the article.

Also I am always open for commenting on Android stuff, so if you feel like talking, contact me on twitter or linkedin.

Источник

HOWTO: Running Java code directly on Android (without creating an APK)

A step by step instruction for compiling a Java program into Android executable and using ADB to run it.

When you want to create a system / commandline tool for Android, you have to write it in C(++)… or do you?

TLDR; here’s the final proof of concept.

Sticking with Java would have the benefit of avoiding all of the native ABI hassle and also being able to call into the Android runtime. So how do we do that?

A (not so) simple Hello World program

Let’s start with the Java program we want to run. In order to make it a bit more interesting (and because any useful program has dependencies), it won’t just print the obligatory “Hello World” message, but also use the Apache Commons CLI library to parse its commandline arguments:

Setting up the working directory

We will have to manually run several commandline tools in the next step, assuming the following final directory structure:

Start by creating an empty directory in a convenient place. Download and unpack the following items there:

Android SDK (either via Android Studio or the SDK Manager). NOTE: If you are an Android developer, you’ll have the Android SDK already installed. In that case, you don’t actually need to copy it to the working directory as long as you know the path to the dx tool.
Apache Commons CLI library v1.3.1

Afterwards copy&paste the HelloWorld code from above into the source folder. You might also find my semantic version parser class useful later on (not required here, though).

Compiling and dexing the Java class

Next step is to compile the java class (keep in mind that Android is stuck with Java 7 — bytecode for later versions won’t work). In case you are not used to doing this outside of an IDE, here’s the command:

Make sure the program compiled properly:

Android cannot run Java class files directly. They have to be converted to Dalvik’s DEX format first (yes, even if you are using ART):

NOTE: Android Build Tools v28.0.2 and later contain a dx upgrade, called d8 . The d8 tool can process Java 8 class files. I’ll stick with dx for backwards compatibility reasons here.

Creating the startup shellscript

Android does not have a (normal) JRE, so JAR files cannot be started the same way as on a PC. You need a shellscript wrapper to do this. Copy&paste the one below to the workspace.

NOTE: DEX files can also be started directly using the dalvikvm command, but going through app_process gives us a pre-warmed VM from the Zygote process (it is also the method employed by framework commands like pm and am ).

Installing and running the (non-) app

Time to push everything to the device:

Moment of truth (fingers crossed):

NOTE: Since nothing was installed into the system, getting rid of the program is simply done by deleting the directory again.

It works, but how do I get a Context?!

Contexts represent an environment that is associated with an app (which we explicitly did not build) and are also device dependant. They can only be created by the ActivityThread class (a hidden system class that you cannot instantiate). If you want to interact with the Android runtime, you have to talk to the system services directly through their Binder interfaces. But that’s a topic for another article.

Источник

Learn Java for Android Development: Introduction to Java

In this tutorial series, you’ll become familiar with Java, the programming language used to develop Android applications. Our goal is to prepare those already familiar with one programming language, such as PHP or Objective-C, to become comfortable working with the Java programming language and dive into Android app development. In this tutorial, you’ll get a brief introduction to Java fundamentals, including object oriented programming, inheritance and more. If you’re new to Java, or just looking to brush up on the details, then this is the tutorial series for you!

Getting Started

As far as prerequisites go, we’re going to assume you understand how to program (perhaps in PHP, or Visual Basic or C++), but that you are unfamiliar with the specifics of programming in the Java language. We aren’t going to teach you to program; we’re going to provide you with clear examples of commonly used Java language constructs and principles, while pointing out some Android-specific tips and tricks.

Читайте также: Моды для сампа андроид

What You’ll Need

Technically, you don’t need any tools to complete this tutorial but you will certainly need them to develop Android applications.

To develop Android applications (or any Java applications, for that matter), you need a development environment to write and build applications. Eclipse is a very popular development environment (IDE) for Java and the preferred IDE for Android development. It’s freely available for Windows, Mac, and Linux operating systems.

For complete instructions on how to install Eclipse (including which versions are supported) and the Android SDK, see the Android developer website.

What is Java?

Android applications are developed using the Java language. As of now, that’s really your only option for native applications. Java is a very popular programming language developed by Sun Microsystems (now owned by Oracle). Developed long after C and C++, Java incorporates many of the powerful features of those powerful languages while addressing some of their drawbacks. Still, programming languages are only as powerful as their libraries. These libraries exist to help developers build applications.

Some of the Java’s important core features are:

It’s easy to learn and understand
It’s designed to be platform-independent and secure, using
virtual machines
It’s object-oriented

Android relies heavily on these Java fundamentals. The Android SDK includes many standard Java libraries (data structure libraries, math libraries, graphics libraries, networking libraries and everything else you could want) as well as special Android libraries that will help you develop awesome Android applications.

Why is Java Easy to Learn?

Java is easy to learn for a variety of reasons. There’s certainly no shortage of Java resources out there to help you learn the language, including websites, tutorials, books, and classes. Java is one of the most widely discussed, taught, and used programming languages on the planet. It’s used for many different types of programming projects, no matter their scale, from web applications to desktop applications to mobile applications.

If you’re coming from a traditional programming background like C or C++, you’ll find Java syntax quite similar. If you’re not, then take comfort in knowing that you’ve chosen one of the easiest languages to learn. You’ll be up and running in no time at all.

Finally, Java is one of the most human-readable languages out there, by which we mean that a person who knows nothing about programming can often look at some Java code and have at least an inkling what it’s doing. Consider the following example:

If you simply read the code aloud, you can pretty much tell that this snippet of code is doing. There’s a single letter variable called character. If the character variable equals the letter a, then we do something (call the doSomething() method), otherwise we do something else (by calling the doSomethingElse() method).

Why is Platform Independence Important?

With many programming languages, you need to use a compiler to reduce your code down into machine language that the device can understand. While this is well and good, different devices use different machine languages. This means that you might need to compile your applications for each different device or machine language—in other words, your code isn’t very portable. This is not the case with Java. The Java compilers convert your code from human readable Java source files to something called “bytecode” in the Java world. These are interpreted by a Java Virtual Machine, which operates much like a physical CPU might operate on machine code, to actually execute the compiled code. Although it might seem like this is inefficient, much effort has been put into making this process very fast and efficient. These efforts have paid off in that Java performance in generally second only to C/C++ in common language performance comparisons.

Android applications run in a special virtual machine called the Dalvik VM. While the details of this VM are unimportant to the average developer, it can be helpful to think of the Dalvik VM as a bubble in which your Android application runs, allowing you to not have to worry about whether the device is a Motorola Droid, an HTC Evo, or the latest toaster running Android. You don’t care so long as the device is Dalvik VM friendly—and that’s the device manufacturer’s job to implement, not yours.

Why is Java Secure?

Let’s take this bubble idea a bit further. Because Java applications run within the bubble that is a virtual machine, they are isolated from the underlying device hardware. Therefore, a virtual machine can encapsulate, contain, and manage code execution in a safe manner compared to languages that operate in machine code directly. The Android platform takes things a step further. Each Android application runs on the (Linux-based) operating system using a different user account and in its own instance of the Dalvik VM. Android applications are closely monitored by the operating system and shut down if they don’t play nice (e.g. use too much processing power, become unresponsive, waste resources, etc.). Therefore, it’s important to develop applications that are stable and responsive. Applications can communicate with one another using well-defined protocols.

Compiling Your Code

Like many languages, Java is still a compiled language even though it doesn’t compile all the way down to machine code. This means you, the developer, need to compile your Android projects and package them up to deploy onto devices. The Eclipse development environment (used with the Android Development plug-in) makes this pretty painless. In Eclipse, automatic compilation is often turned on by default. This means that every time you save a project file, Eclipse recompiles the changes for your application package. You immediately see compile errors. Eclipse also interprets Java as you type, providing handy code coloring and formatting as well as showing many types of errors as you go. Often, you can click on the error and have Eclipse automatically fix a typo, or add an import statement, or provide a method stub for you, saving lots of typing.

You can still manually compile your code if you so desire. Within Eclipse, you’ll find the Build settings under the project menu. If you have “Build Automatically” turned on, you can still choose the “Clean…” option that will allow you to do full rebuild of all files. If “Build Automatically” is turned off, “Build All” and “Build Project” menu options are enabled. «Build All» means to build all of the projects in the workspace. You can have many projects in an Eclipse workspace.

The build process, for regular Java projects, results in a file with the extension of JAR – Java ARchive. Android applications take JAR files and package them for deployment on devices as Android PacKage files with an extension .apk. These formats not only include your compiled Java code, but also any other resources, such as strings, images, or sound files, that your application requires to run as well as the Application Manifest file, AndroidManifest.xml. The Android Manifest file is a file required by all Android applications, which you use to define configuration details about your app.

What is an Object Oriented Programming Language?

Okay. Time for a very brief and 20,000 foot view of object oriented programming (OOP). OOP is a programming style or technique that relies upon the definition of data structures called objects. For those new to OOP, an object can be thought of much like a custom data type. For example, you might have a Dog object, which represents the blueprint for a generic dog, with a name, breed, and gender. You could then create different instances of the Dog object to represent specific dogs. Each Dog object must be created by calling its constructor (a method that has the same name as the object itself, and may or may not have parameters for setting initial values). For example, the following Dog objects use a constructor with three parameters (name, breed, gender):

So where is this Dog object defined? Well, here we need to begin defining some of the fundamental building blocks of the Java programming language. A class provides a definition for an object. Therefore, there is a Dog class somewhere—either defined by you or in some library somewhere. Generally speaking, a class will be defined in its own file, with the filename matching the class name (e.g. Dog.java). There are exceptions to this rule, such as classes defined within other classes (when a class is declared within a class, it is generally defined for use within the parent class only as a helper class, and referred to as an inner class).

When you want to reference an object from within another class, you need to include an import statement in the top of your class file, much like you would use a #include statement in a compiled language like C.

A class typically describes the data and behavior of an object. The behavior is defined using class methods. Method is the common term for a subroutine in an OOP language. Many common object classes are defined in shared class libraries like software development kits (SDKs), whereas others are defined by you, the developer, for your own purposes. Software is then built up by using and manipulating object instances in different ways.

Please realize this is a very generalized definition of OOP. There are entire books written on this subject. If you’d like to know more about OOP, here are a few resources you might want to check out:

Note: We use a lot of different terminology in this tutorial. There are multiple ways to refer to a given concept (e.g. superclass vs. parent class), which is confusing to those new to object oriented programming. Different developers use different terms, and so we have tried to mention synonyms where appropriate. Deciding which terms you will use is a personal choice.

Understanding Inheritance

Here is another important Java concept you’ll run into a lot: inheritance. Simply put, inheritance means that Java classes (and therefore objects) can be organized into hierarchies with lower, more specific, classes in the hierarchy inheriting behavior and traits from higher, more generic, classes.

This concept is best illustrated by example. Let’s pretend we are developing a Java application to simulate an aquarium. This aquarium has some fish in it. Therefore, we might define a class to represent a fish. This class, called Fish, could include some data fields (also called attributes, or class member variables) to describe a fish object: species, color and size; as well as some of its behavior in the form of methods (also called subroutines, or functions in procedural languages), like eat(), sleep(), and makeBabyFish().

A special type of method, called a constructor, is used to create and initialize an object; constructors are named the same as their class and may include parameters. The following Fish class has two constructors: one for creating a generic Fish object and another for constructing a specific Fish object with some initial data. You’ll also see that the Fish class has two eat() methods: one for eating something random, and another for eating another fish, which would be represented by another instance of the Fish class:

Classes can be organized into hierarchies, where a derived class (or subclass) includes all the features of its parent class (or superclass), but refines and adds to them to define a more specific object using the extends keyword. This is called inheritance.

For example, the Fish class might have two subclasses: FreshwaterFish and SaltwaterFish. These subclasses would have all the features of the Fish class, but could further customize the objects through new attributes and behaviors or modified behaviors from the parent class Fish. For example, the FreshwaterFish class might include information about the type of freshwater environment lived in (e.g. river, lake, pond, or puddle). Similarly, the SaltwaterFish class might customize the makeBabyFish() method such that the fish eats its mate after breeding (as defined in the super class) by using the override mechanism, like this:

Organizing Object Behavior with Interfaces

In Java, you can organize object behaviors in what are called interfaces. While a class defines an object, an interface defines some behavior that can be applied to an object. For example, we could define a Swimmer interface that provides a set of methods that are common across all objects that can swim, whether they are fish, otters, or submergible androids. The Swimmer interface might specify four methods: startSwimming(), stopSwimming(), dive(), and surface().

A class like Fish could then implement the Swimmer interface (using the implements keyword) and provide implementations of the swimming behavior:

Organizing Classes and Interfaces with Packages

Class hierarchies, such as our fish classes, can then be organized into packages. A package is simply a set of classes and interfaces, bundled together. Developers use namespaces to uniquely name packages. For example, we could use com.mamlambo.aquarium or com.ourclient.project.subproject as our package name to keep track of our fish-related classes.

Wrapping Up

Wow! You’ve just embarked on a crash-course in Java for Android development. We’ve covered a pretty intense amount of material here, so let things settle for a bit before moving on to the next lesson of this tutorial series. In Lesson 2, we switch our focus to the nitty-gritty details of Java syntax.

You’ve only scratched the surface of Java development for Android development. Check out all the other great tutorials on Mobiletuts+ to dive deeper into Java and Android development. Good luck!

About the Authors

Mobile developers Lauren Darcey and Shane Conder have coauthored several books on Android development: an in-depth programming book entitled Android Wireless Application Development and Sams TeachYourself Android Application Development in 24 Hours. When not writing, they spend their time developing mobile software at their company and providing consulting services. They can be reached at via email to androidwirelessdev+mt@gmail.com, via their blog at androidbook.blogspot.com, and on Twitter @androidwireless.

Need More Help Writing Android Apps? Check out our Latest Books and Resources!

Useful Resources:

If you want to get started with Android development, an Android app template is a great place to start. Check out the selection on Envato Market—or you could look more specifically for Java items.

Android app templates on Envato Market

You can also find Android developers on Envato Studio to help you with everything from UI design to creating a native Android app.

Android developers on Envato Studio

Источник

Compiling java code on android