Difference between revisions of "Language - Java"

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By following the instructions for your operating system and compiler above, you probably now have a working example and want to understand it better so you can change it to do what you want.  This teaching section has resources for you to learn from the examples and write your own.
 
By following the instructions for your operating system and compiler above, you probably now have a working example and want to understand it better so you can change it to do what you want.  This teaching section has resources for you to learn from the examples and write your own.
  
Next, comes our API information.  These resources outline the Phidgets Java methods:
+
Your main reference for writing Java code will be our Java API information, with syntax for all of our functions:
  
 
{{UsingAPhidgetInCodeGeneral|both of which are available in Java|[http://www.phidgets.com/documentation/JavaDoc.zip Java API]}}
 
{{UsingAPhidgetInCodeGeneral|both of which are available in Java|[http://www.phidgets.com/documentation/JavaDoc.zip Java API]}}

Revision as of 21:14, 25 April 2012

Java

Java is a modern, object-oriented programming language maintained by Oracle.


Introduction

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Quick Downloads

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Getting started with Java

If you are new to writing code for Phidgets, we recommend starting by running, then modifying existing examples. This will allow you to:

  • Make sure your libraries are properly linked
  • Go from source code to a test application as quickly as possible
  • Ensure your Phidget is hooked up properly

Instructions are divided up by operating system. Choose:

Windows (2000/XP/Vista/7)

Description of Library Files

Java programs on Windows depend on two files, which the installers in the Quick Downloads section put onto your system:

  • phidget21.dll contains the actual Phidget library, which is used at run-time. By default, it is placed in C:\Windows\System32.
  • phidget21.jar is the Phidget Java library for JDK 1.4.2 or higher. Your compiler has to know where this file is. By default, it is placed into C:\Program Files\Phidgets. So, you can either point your compiler to that location, or copy and link to it in a directory for your project workspace. For more information, please see the section for your specific compiler/environment.

If you do not want to use our installer, you can download the phidget21.dll as well as the phidget21.jar and manually install them where you want; refer to our Manual Installation Instructions.

Running the examples and writing your own code can be fairly compiler-specific, so we include instructions for each compiler below.

You can program Phidgets with Java in command line with the javac compiler as well as in IDEs such as NetBeans and Eclipse.

Javac (Command Line)

Use Our Examples

Download the example and unpack them into a folder. Here, you can find example programs for all the devices. If you aren't sure what the software example for your device is called, check the software object listed in the Getting Started guide for your device. Please only use the simple examples. The full examples are intended for the NetBeans IDE.

Ensure that the phidget21.jar is in the same directory as the source code.

To compile in Windows command prompt:

javac -classpath .;phidget21.jar example.java

This will create Java bytecode in the form of .class files. Type the following to run the program:

java -classpath .;phidget21.jar example


If you wish, you can compile the project as a .jar so there are fewer files to maintain. The [Java SDK] provides the jar utility which packages all the .class files into a single .jar file. To begin, you will have to provide a Manifest file to indicate the program entry point. With your favourite text editor, create a new file with the following content:

Manifest-Version: 1.0
Class-Path: phidget21.jar
Main-Class: example


Ensure that the file ends in a single new line or a carriage return character. Save the file as example.mf and place it in the same directory as the other .class files. Next, create the .jar with:

jar -cfm example.jar example.mf *.class

Afterwards, you can run the .jar with:

java -jar example.jar

Once you have the Java examples running, we have a teaching section below to help you follow them.

Write Your Own Code

When you are building a project from scratch, or adding Phidget function calls to an existing project, you'll need to configure your development environment to properly link the Phidget Java library. Please see the previous section for instructions.

In your code, you will need to include the Phidget Java library:

import com.phidgets.*;
import com.phidgets.event.*;

The project now has access to the Phidget function calls and you are ready to begin coding.

The same teaching section which describes the examples also has further resources for programming your Phidget.

NetBeans

Use Our Examples

You first download the examples, unpack them into a folder, and then find the source code for your device. The source file will be named the same as the software object for your device. If you aren't sure what the software example for your device is called, check the software object listed in the Getting Started guide for your device. The full examples were written in NetBeans, so the rest of this section will use these examples. To use the simple examples, you will have to import the source code into a new NetBeans project.

Open Project

The only thing left to do is to run the examples! Click on Run → Run Project. The project, by default tries to find the phidget21.jar in ..\..\lib.

Run

Once you have the Java examples running, we have a teaching section below to help you follow them.

Write Your Own Code

When you are building a project from scratch, or adding Phidget function calls to an existing project, you'll need to configure your development environment to properly link the Phidget Java library. To begin:

1. Create a new Java application project with a descriptive name such as PhidgetTest.

New Project

2. Add a reference to the Phidget Java library. In the projects pane, right click Libraries and add the jar.

Add Jar

3. Find and select phidget21.jar.

Add Jar

4. Then, in your code, you will need to include the Phidget Java library:

import com.phidgets.*;
import com.phidgets.event.*;


The project now has access to the Phidget function calls and you are ready to begin coding.

The same teaching section which describes the examples also has further resources for programming your Phidget.

Eclipse

Use Our Examples

1. Download the examples and unpack them into a folder. Here, you can find example programs for all the devices. If you aren't sure what the software example for your device is called, check the software object listed in the Getting Started guide for your device. Please use the simple examples. The full examples were written in NetBeans, and are not compatible with Eclipse. The rest of this guide will assume that the simple examples are used. The example source code will be copied into your Eclipse project later on. Keep note of the file name of the example as a Java class will be created with the same name.

2. Generate a new Java project with a descriptive name such as PhidgetTest. Click next.

New Project

3. On the next screen, go to the libraries panel and add an external jar.

Add Jar

4. Find and select phidget21.jar.

Add Jar

5. Add a new Java class to the project.

New Class

6. Name this class with the same name as the simple example's name.

New Class

7. Copy and paste the example source code over to the class you created.

Source Code

8. The only thing left to do is to run the examples!

Run


Once you have the Java examples running, we have a teaching section below to help you follow them.

Write Your Own Code

When you are building a project from scratch, or adding Phidget function calls to an existing project, you'll need to configure your development environment to properly link the Phidget Java library. Please see the Use Our Examples section for instructions.

In your code, you will need to include the Phidget Java library:

import com.phidgets.*;
import com.phidgets.event.*;

The project now has access to the Phidget function calls and you are ready to begin coding.

The same teaching section which describes the examples also has further resources for programming your Phidget.

Mac OS

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Java has excellent support on OS X through the Java Compiler.

The first step in using Java on Mac is to install the Phidget libraries. Compile and install them as explained on the getting started guide for your device. Then, the OS - OS X page also describes the different Phidget files, their installed locations, and their roles....

Use Our Examples

The command to compile in a OS X and Linux terminal are slightly different. Rather than prefixing phidget21.jar with a semi-colon( ; ), a colon( : ) is used:

javac -classpath .:phidget21.jar example.java

Then, to run the program:

java -classpath .:phidget21.jar example

Perhaps refer to the Windows section of Eclipse and Netbeans for further information?

Write Your Own Code

Linux

Java has excellent support on Linux - there is an established implementation of the Java compiler and interpreter, and several Integrated Development Environments (IDEs) including NetBeans and Eclipse.

The first step in using Java on Linux is to install the base Phidget libraries. Compile and install them as explained on the main Linux page. That Linux page also describes the different basic Phidget library files, their installed locations, and their roles.

You will also need the Phidget Java Libraries (phidget21.jar).

Once downloaded, the phidget21.jar library file does not get 'installed' (i.e. do not run java -jar phidget21.jar). Rather, the library file gets put into the path of whatever program you write, and you will link it via both the java compiler and the java interpreter. We walk you through this below.

We have two different types of Phidget examples in Java:

  • Simple examples, to be run on the command line, and
  • Full examples, to be run in NetBeans

Both are contained within the Phidget Java example download package.

Description of Library Files

The Phidget Java libraries depend on the C libraries being installed as explained on the main Linux page. If you browse around within the phidget21.jar archive, you will find Java class files (too many to reasonably list here) that have names related to the devices they provide an API for.

These Java class files use the functions available in the dynamic Phidget21 C-language library on Linux. Dynamic libraries end with .so, and so the C library that the Phidget Java class files use is /usr/lib/libphidget21.so.

Javac (Command Line)

Use Our Examples

Linux gets somewhat complicated in that two Java compilers exist: openjdk and gcj. Furthermore, a given IDE can usually use either compiler. That being said, we only offer support here for openJDK and IDEs running openJDK.

To find out which type of compiler your computer has, use the -version option on the command line. You can use the same option for your runtime environment (interpreter):

$> java -version
java version "1.6.0_23"
OpenJDK Runtime Environment (IcedTea6 1.11pre) (6b23~pre11-0ubuntu1.11.10.1)
OpenJDK 64-Bit Server VM (build 20.0-b11, mixed mode)

$> javac -version
javac 1.6.0_23

The good news is that you can have both openjdk and gcj on your machine, co-habitating happily. There can be only one linked java and javac in /usr/bin/ however, and so this will correspond to whichever java compiler and interpreter you installed last.

If you do not have openjdk installed already (this is the default Java installation for most Linux machines, so you will probably know), and you choose to install it for Phidget purposes, it is important is that the java version be greater than the javac version. Otherwise, your runtime environment will consider the stuff your compiler produces to be newfangled nonsense. So when installing Java from a repository, you should install both the jdk and the jre. These are, unfortunately, usually separate packages in a repository (e.g. openjdk-7-jre and openjdk-7-jdk).

The simple examples in Java are meant to be compiled and run on the command line. The example package includes a Makefile so you can either make all of the examples at once, with:

make all

...Or you can make them individually. You should pick out the example with the name that corresponds to the family of your Phidget hardware. If you're not sure what the family (software object) is, you can find out on the product API for your device. Once you've identified the right example - say, HelloWorld.java, which will work with any Phidget - compile it on the command line with:

javac -classpath .:phidget21.jar HelloWorld.java

To run the example on a Linux machine without your udev USB rules set, you will need to run the Java example as root:

sudo java -classpath .:phidget21.jar HelloWorld

Write Your Own Code

You'll note that the Phidget Java library file phidget21.jar needs to be explicitly linked at both points in the compile and run process. Alternatively, you can make a jar file which includes the Phidget Java library. This process takes two steps, the first of which is creating a text file called MyProgram.mf, where MyProgram is replaced by the name of your main class in both the filename and the text below:

Manifest-Version: 1.0
Class-Path: phidget21.jar
Main-Class: MyProgram

Note: The manifest file should end with a carriage return. So, there should be an extra line at the bottom of the file.

After creating the manifest file, you can use the jar function to create one self-contained file with your classes and the correct classpath.

jar –cfm MyProgram.jar MyProgram.mf *.class

If porting this for an external system, such as one that your customer would be running, the Phidget library would need to be compiled and distributed along with the .jar. Although we do not directly support this, if you are interested in how to construct this, we provide both a distribution example and information on cross-compiling:

  • The Android Java libraries have an ARM-compiled libphidget21.so file included, as an example of distributing a compiled libphidget21.so with the jar file
  • The Linux page has more detail for compiling the Phidget C Libraries for an external target.

NetBeans

We offer in-depth tutorials on using our examples in NetBeans and Eclipse in the Windows NetBeans and Windows Eclipse sections.

As our full examples are written with NetBeans, but NetBeans is not part of the standard Linux package repository, we offer installation instructions here before referring to the Windows sections.

Installation

Although Eclipse is standard in the Debian/Ubuntu package repository, NetBeans is no longer standard. What is more, Netbeans does not install by default into a folder within your path. As our Phidget full Java examples are written using NetBeans, we provide basic installation instructions here so you can actually run them.

To install NetBeans:

1. Download the install script from website: http://netbeans.org/downloads/
2. Change the permissions of the downloaded file to be executable. Usually, this is something like:

chmod +x netbeans-7.1-ml-javase-linux.sh

3. Run the downloaded file as a script. (This will result in a GUI interaction that walks you through installation.)
4. To find the location where the NetBeans installation occurred, run:

updatedb
locate netbeans

5. Usually, the location of the binary is /usr/local/netbeans-7.1/bin/netbeans, where 7.1 is the installed version.

Use Our Examples

Once you have NetBeans installed, running our examples will be very similar to the process described in the Windows NetBeans section.

Write Your Own Code

When you are building a project from scratch, or adding Phidget function calls to an existing project, you'll need to configure your development environment to properly link the Phidget Java library. Please see the Windows NetBeans section for instructions if you are unfamiliar with NetBeans.

In your code, you will need to include the Phidget Java library:

import com.phidgets.*;
import com.phidgets.event.*;

The project now has access to the Phidget function calls and you are ready to begin coding.

The teaching section - which describes the examples - also has further resources for programming your Phidget.

Follow the Examples

By following the instructions for your operating system and compiler above, you probably now have a working example and want to understand it better so you can change it to do what you want. This teaching section has resources for you to learn from the examples and write your own.

Your main reference for writing Java code will be our Java API information, with syntax for all of our functions:

Template:UsingAPhidgetInCodeGeneral

Example Flow

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Common Problems and Solutions/Workarounds

None yet.