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Can I use a Java library in an iOS app using Cordova?

I would like to use the Ionic or other cross-platform framework to build a mobile app. In this app I would like to use a Java library. From what I understand, I can use this Java library in my hybrid app if I write a Cordova wrapper for the library. But I have not been able to find a way to use the Java library on iOS. Is this possible?

You can't, iOS apps don't understand Java, even if you write a Cordova plugin. Is there no iOS alternative of the library you want to use?
Using Cordova you could build a plugin that uses the library you want to use on Android and use a different library on iOS. In your Ionic app, if the plugin is well written, you will be able to call the same function and the plugin will handle the rest.
Regarding this:
I've found that in android once you wirte a Cordova wrapper for the
library it can be used within the app even though I don't really
understand what it really means.
Cordova allows you to call native functions using JavaScript, so without Cordova you won't be able to use the Java library, but by building a plugin using Cordova you can. Here is a tutorial on how to create a Cordova plugin and here is another. I also recommend looking at existing Cordova plugins to see how it is done. If you share the library, we may also be able to help you create the plugin.

You can use Java code if you use Codename One's Cordova compatibility for portability.
Notice you can't use a binary jar "as is" but you can use Java source code which will work natively on iOS.

How can I run python script in android studio with java [duplicate]

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We are working on an S60 version and this platform has a nice Python API..
However, there is nothing official about Python on Android, but since Jython exists, is there a way to let the snake and the robot work together??

One way is to use Kivy:
Open source Python library for rapid development of applications
that make use of innovative user interfaces, such as multi-touch apps.
Kivy runs on Linux, Windows, OS X, Android and iOS. You can run the same [python] code on all supported platforms.
Kivy Showcase app

There is also the new Android Scripting Environment (ASE/SL4A) project. It looks awesome, and it has some integration with native Android components.
Note: no longer under "active development", but some forks may be.

Yes! : Android Scripting Environment
An example via Matt Cutts via SL4A -- "here’s a barcode scanner written in six lines of Python code:
import android
droid = android.Android()
code = droid.scanBarcode()
isbn = int(code['result']['SCAN_RESULT'])
url = "http://books.google.com?q=%d" % isbn
droid.startActivity('android.intent.action.VIEW', url)

Pygame Subset for Android
Pygame is a 2D game engine for Python (on desktop) that is popular with new programmers. The Pygame Subset for Android describes itself as...
...a port of a subset of Pygame functionality to the Android platform. The goal of the project is to allow the creation of Android-specific games, and to ease the porting of games from PC-like platforms to Android.
The examples include a complete game packaged as an APK, which is pretty interesting.

As a Python lover and Android programmer, I'm sad to say this is not a good way to go. There are two problems:
One problem is that there is a lot more than just a programming language to the Android development tools. A lot of the Android graphics involve XML files to configure the display, similar to HTML. The built-in java objects are integrated with this XML layout, and it's a lot easier than writing your code to go from logic to bitmap.
The other problem is that the G1 (and probably other Android devices for the near future) are not that fast. 200 MHz processors and RAM is very limited. Even in Java, you have to do a decent amount of rewriting-to-avoid-more-object-creation if you want to make your app perfectly smooth. Python is going to be too slow for a while still on mobile devices.

Scripting Layer for Android
SL4A does what you want. You can easily install it directly onto your device from their site, and do not need root.
It supports a range of languages. Python is the most mature. By default, it uses Python 2.6, but there is a 3.2 port you can use instead. I have used that port for all kinds of things on a Galaxy S2 and it worked fine.
API
SL4A provides a port of their android library for each supported language. The library provides an interface to the underlying Android API through a single Android object.
from android import Android
droid = Android()
droid.ttsSpeak('hello world') # example using the text to speech facade
Each language has pretty much the same API. You can even use the JavaScript API inside webviews.
let droid = new Android();
droid.ttsSpeak("hello from js");
User Interfaces
For user interfaces, you have three options:
You can easily use the generic, native dialogues and menus through the
API. This is good for confirmation dialogues and other basic user inputs.
You can also open a webview from inside a Python script, then use HTML5
for the user interface. When you use webviews from Python, you can pass
messages back and forth, between the webview and the Python process that
spawned it. The UI will not be native, but it is still a good option to
have.
There is some support for native Android user interfaces, but I am not
sure how well it works; I just haven't ever used it.
You can mix options, so you can have a webview for the main interface, and still use native dialogues.
QPython
There is a third party project named QPython. It builds on SL4A, and throws in some other useful stuff.
QPython gives you a nicer UI to manage your installation, and includes a little, touchscreen code editor, a Python shell, and a PIP shell for package management. They also have a Python 3 port. Both versions are available from the Play Store, free of charge. QPython also bundles libraries from a bunch of Python on Android projects, including Kivy, so it is not just SL4A.
Note that QPython still develop their fork of SL4A (though, not much to be honest). The main SL4A project itself is pretty much dead.
Useful Links
SL4A Project (now on GitHub): https://github.com/damonkohler/sl4a
SL4A Python 3 Port: https://code.google.com/p/python-for-android/wiki/Python3
QPython Project: http://qpython.com
Learn SL4A (Tutorialspoint): https://www.tutorialspoint.com/sl4a/index.htm

Cross-Compilation & Ignifuga
My blog has instructions and a patch for cross compiling Python 2.7.2 for Android.
I've also open sourced Ignifuga, my 2D Game Engine. It's Python/SDL based, and it cross compiles for Android. Even if you don't use it for games, you might get useful ideas from the code or builder utility (named Schafer, after Tim... you know who).

Termux
You can use the Termux app, which provides a POSIX environment for Android, to install Python.
Note that apt install python will install Python3 on Termux. For Python2, you need to use apt install python2.
Some demos: https://www.youtube.com/watch?v=fqqsl72mASE
The GitHub project: https://github.com/termux

Kivy
I wanted to add to what #JohnMudd has written about Kivy. It has been years since the situation he described, and Kivy has evolved substantially.
The biggest selling point of Kivy, in my opinion, is its cross-platform compatibility. You can code and test everything using any desktop environment (Windows/*nix etc.), then package your app for a range of different platforms, including Android, iOS, MacOS and Windows (though apps often lack the native look and feel).
With Kivy's own KV language, you can code and build the GUI interface easily (it's just like Java XML, but rather than TextView etc., KV has its own ui.widgets for a similar translation), which is in my opinion quite easy to adopt.
Currently Buildozer and python-for-android are the most recommended tools to build and package your apps. I have tried them both and can firmly say that they make building Android apps with Python a breeze. Their guides are well documented too.
iOS is another big selling point of Kivy. You can use the same code base with few changes required via kivy-ios Homebrew tools, although Xcode is required for the build, before running on their devices (AFAIK the iOS Simulator in Xcode currently doesn't work for the x86-architecture build). There are also some dependency issues which must be manually compiled and fiddled around with in Xcode to have a successful build, but they wouldn't be too difficult to resolve and people in Kivy Google Group are really helpful too.
With all that being said, users with good Python knowledge should have no problem picking up the basics quickly.
If you are using Kivy for more serious projects, you may find existing modules unsatisfactory. There are some workable solutions though. With the (work in progress) pyjnius for Android, and pyobjus, users can now access Java/Objective-C classes to control some of the native APIs.

Using SL4A (which has already been mentioned by itself in other answers) you can run a full-blown web2py instance (other python web frameworks are likely candidates as well). SL4A doesn't allow you to do native UI components (buttons, scroll bars, and the like), but it does support WebViews. A WebView is basically nothing more than a striped down web browser pointed at a fixed address. I believe the native Gmail app uses a WebView instead of going the regular widget route.
This route would have some interesting features:
In the case of most python web frameworks, you could actually develop and test without using an android device or android emulator.
Whatever Python code you end up writing for the phone could also be put on a public webserver with very little (if any) modification.
You could take advantage of all of the crazy web stuff out there: query, HTML5, CSS3, etc.

Not at the moment and you would be lucky to get Jython to work soon. If you're planning to start your development now you would be better off with just sticking to Java for now on.

QPython
I use the QPython app. It's free and includes a code editor, an interactive interpreter and a package manager, allowing you to create and execute Python programs directly on your device.

Here are some tools listed in official python website
There is an app called QPython3 in playstore which can be used for both editing and running python script.
Playstore link
Another app called Termux in which you can install python using command
pkg install python
Playstore Link
If you want develop apps , there is Python Android Scripting Layer (SL4A) .
The Scripting Layer for Android, SL4A, is an open source application that allows programs written in a range of interpreted languages to run on Android. It also provides a high level API that allows these programs to interact with the Android device, making it easy to do stuff like accessing sensor data, sending an SMS, rendering user interfaces and so on.
You can also check PySide for Android, which is actually Python bindings for the Qt 4.
There's a platform called PyMob where apps can be written purely in Python and the compiler tool-flow (PyMob) converts them in native source codes for various platforms.
Also check python-for-android
python-for-android is an open source build tool to let you package Python code into standalone android APKs. These can be passed around, installed, or uploaded to marketplaces such as the Play Store just like any other Android app. This tool was originally developed for the Kivy cross-platform graphical framework, but now supports multiple bootstraps and can be easily extended to package other types of Python apps for Android.
Try Chaquopy
A Python SDK for Android
Anddd... BeeWare
BeeWare allows you to write your app in Python and release it on multiple platforms. No need to rewrite the app in multiple programming languages. It means no issues with build tools, environments, compatibility, etc.

From the Python for android site:
Python for android is a project to create your own Python distribution including the modules you want, and create an apk including python, libs, and your application.

Chaquopy
Chaquopy is a plugin for Android Studio's Gradle-based build system. It focuses on close integration with the standard Android development tools.
It provides complete APIs to call Java from Python or Python from Java, allowing the developer to use whichever language is best for each component of their app.
It can automatically download PyPI packages and build them into an app, including selected native packages such as NumPy.
It enables full access to all Android APIs from Python, including the native user interface toolkit (example pure-Python activity).
This used to be a commercial product, but it's now free and open-source.
(I am the creator of this product.)

Yet another attempt: https://code.google.com/p/android-python27/
This one embed directly the Python interpretter in your app apk.

You can run your Python code using sl4a. sl4a supports Python, Perl, JRuby, Lua, BeanShell, JavaScript, Tcl, and shell script.
You can learn sl4a Python Examples.

You can use QPython:
It has a Python Console, Editor, as well as Package Management / Installers
http://qpython.com/
It's an open source project with both Python 2 and Python 3 implementations. You can download the source and the Android .apk files directly from github.
QPython 2: https://github.com/qpython-android/qpython/releases
QPython 3: https://github.com/qpython-android/qpython3/releases

Another option if you are looking for 3.4.2 or newer (3.9.6 as of this writing) is this archive on GitHub.
Python3-Android 3.4.2 or Python3-Android 3.9.6
I believe the original archive supports Python 3.4.2, the latest GRRedwings branch support 3.9.6 and the 22b version of the NDK. Older branches support other versions, but are not as easy to compile with docker.
The older version you simply clone the archive, run make and you get the .so or the .a
The newer versions follow the ReadMe, but it uses docker for consistent builds.
I currently use this to run raw Python on android devices. With a couple modifications to the build files you can also make x86 and armeabi 64 bit

Take a look at BeeWare. It has grown significantly. It is awarded with PSF (Python Software Foundation) Education Grant.
Beeware's aim is to be able to create native apps with Python for all supported operating systems, including Android.
Official Website: Beeware
Github Repo: https://github.com/beeware

Didn't see this posted here, but you can do it with Pyside and Qt now that Qt works on Android thanks to Necessitas.
It seems like quite a kludge at the moment but could be a viable route eventually...
http://qt-project.org/wiki/PySide_for_Android_guide

One more option seems to be pyqtdeploy which citing the docs is:
a tool that, in conjunction with other tools provided with Qt, enables
the deployment of PyQt4 and PyQt5 applications written with Python
v2.7 or Python v3.3 or later. It supports deployment to desktop
platforms (Linux, Windows and OS X) and to mobile platforms (iOS and
Android).
According to Deploying PyQt5 application to Android via pyqtdeploy and Qt5 it is actively developed, although it is difficult to find examples of working Android apps or tutorial on how to cross-compile all the required libraries to Android. It is an interesting project to keep in mind though!

Check out enaml-native which takes the react-native concept and applies it to python.
It lets users build apps with native Android widgets and provides APIs to use android and java libraries from python.
It also integrates with android-studio and shares a few of react's nice dev features like code reloading and remote debugging.

Porting of Qt code on Android and how it works

I was thinking of porting my Qt application on android.
My question is how a code written in C++ and Qt which is also a C++ library gets ported to android as android requires java code and an apk file is needed to install the app on device. I am curious as to how and what things they do on the code to make it work like a java code.
If the question is not clear , please comment and i will do my best to make it more clear.

Android applications are Java applications, running on a virtual machine called “Dalvik”. This causes many challenges for a Qt/C++ application to run on such a Java based platform. To ovecome this, a Qt for Android application has two parts. The first part is your Qt/C++ native application which is organized by qmake. The second part is a launcher which is a Java code generated by Qt Creator automatically based on your application preferences, settings and target Android version.
The launcher is a Java process, so Qt Android applications have a Java-based entry point. The Java code in launcher will load the required Qt libraries, based on the meta-information given in other files in the template. So when a Qt for Android application is started, it's just a regular Java application. The entry point will be in QtActivity.java which can be found under android/src/… in your project build directory.
After loading the Qt libraries, the Java code will start the application's native main() function on a new thread and the application will launch. At this point, the Java code is used to delegate events from Android into Qt. Qt for Android applications use "Java Native Interface" (JNI) to communicate between Java world and C++ world.

Just use Qt5.4.0 and install NDK+android SDK you will find it's very easy that you can use c++ on Android.

Porting C code to Android

I am at the very start of a project where we are trying to write an application for an android smartphone that will call a shared library written in C.
It seems that the way to do this is to use the Android NDK to build the library in a binary format compatible with the smartphone hardware then use JNI to call the shared library from Java. Possibly using SWIG along the way to facilitate with the JNI wrapper functions.
But before I go down this route, am I missing any, potentially much simpler, approaches to getting a C app to run on a smartphone? What got me thinking that there may be other alternatives was the Canonical project looking to run ubuntu on a smartphone (http://www.ubuntu.com/devices/android) but it doesn't seem to be available yet.
Any lateral thoughts on this topic gratefully received

As far as I know, the NDK is the preferred route to follow when using native code in android. You can also build a java wrapper library around your C code, separate from your Android project, and include that .jar in your Android app. This uses standard Java instead of Google's NDK, and I have used several libraries built in this manner in android with very little effort.

Android application development: java vs. jquery mobile

I'd like to build an android application for a school project but I'm a bit confused, I saw that i can build an application using Java or using Jquery mobile.
Do they have the same capabilities?
If i build an application using Jquery , can i pack it and have it installed like a java application (as apk) or is it only used for building websites?
If so, what tool do i use to pack it?

jQuery Mobile needs an intermediary framework that communicates between JavaScript and Java. PhoneGap is a popular one of these frameworks.
PhoneGap is also actively maintained and they roll out new versions almost every month.
The main reason to use PhoneGap/jQuery Mobile is that it makes development easy if you already know HTML/JS/CSS. Another great reason to use PhoneGap is that you can use your existing website as the base for native applications, yeah, plural, not just Android but also iOS, Blackberry, etc. It also gives you a pre-built UI with some widgets so you don't have to roll your own.
The jQuery Mobile documentation talks about some of the caveats to creating a native application with PhoneGap and jQuery Mobile.

I don't know what you have already tried or what your skill set is (based on your stackoverflow history you may know more about java than I do), but you would be best off just using the Android SDK. I was able to design and complete a custom business project and learn java while doing it. I can't comment much on jQuery since I've never used it. jQuery seems like it might be a nice for the reasons Jasper listed but might add layers of complexity you don't need to deal with if you don't need to run your app on other platforms.

Jquery Mobile Framework provides the way how you web application looks on different hand held devices simply but this can not use the native device capabilities like picking up an contact from the contact book/application. while native application has the capabilities to handle all the system generated events or broadcasts.