I'm trying to learn JNI on Windows 7 64-bit, but JDK 8 does not include javah.exe. I tried both the 32-bit and 64-bit versions. The Oracle documentation shows that javah is part of JDK 8 and doesn't make any platform distinction. Is there a separate download for JNI?
Also, the tutorials that I could find on JNI on Windows are pretty old - is there a newer way to do JNI in Windows, or does anyone have any suggestions for current Windows JNI Tutorials? NetBeans is my preferred IDE, but I'm not exclusive.
Hej Kevin, there is no seperate download needed for JNI and javah.exe is included in your JDK, search for it in %JAVA_HOME%/bin (if you don't have set this environment variable, look into C:\Program Files\Java\jdk1.8.0_121\bin or the version you have). Make sure you have downloaded the JDK, not JRE. And, the best JNI tutorial to start with is indeed that one, at least for me it was.
Related
I wanted to install J2ME and configure it with Netbeans. I followed two different tutorials word by word but somehow mine would give me many errors. After so much searching I realized that the JDK, Netbeans and J2ME must all be of the same level ie. all to be of x32 or all to be of x64. Now, how do I know what level is each of them at?
How do I know if NetBeans is x32 or x64, as well as JDK and J2ME?
I am using JDK 1.8, Netbeans 8.2, J2ME 3.4
For Java, you can do java -version, and it'll tell you what version you have.
I did a quick look around for the other two but couldn't find anything immediately. However, if you search something like "check bit version for Netbeans/J2ME" then you might get it.
Another way to figure out would be based on your OS. Depending on how new/old it is, it might require certain bit version. You probably installed the correct one (or you should uninstall and re-install the correct one based on their respective installation guide), so you should know what bit version when you first installed.
For Netbeans and J2ME just open them, then open the Task Manager. On the list of Apps, the version of the software is shown as shown below.
About JDK, Open your C Drive and look for the installation folder of your JDK. If it is installed in the Program File folder then it is x64, if it is in the Program File(x86) then it is x32.
I've just installed Eclipse, after i installed the java JDK.
The Getting Started guide (in Eclipse) says i should reference my JDK installation in Window>Preferences>Java>Installed JREs, but that a JRE would also work.
Select the Java > Installed JREs preference page to display the installed Java Runtime Environments. Confirm that a JRE has been detected. By default, the JRE used to run the workbench will be used to build and run Java programs. It should appear with a checkmark in the list of installed JREs. We recommend that you use a Java SDK instead of a JRE. An SDK is designed for development and contains the source code for the Java library, easing debugging.
There was already a JRE set up there (not a JDK), so i did nothing and tried to compile a Hello World (just to see what would happen). To my surprise, it compiled!
I searched a little bit and it looks like this works because Eclipse has a built-in Java Compiler. I tried debugging using the same eclipse set up, and it was also successful.
So, what is the difference between setting a JDK and JRE there? Why is it important to download the JDK, since in my default configuration Eclipse doesn't seem to use it?
Probably the main difference is you get the source to all of the Java runtime libraries (with the JDK) which can be a big help. I always use the JDKs for that reason.
Also if you are debugging, this will allow you to meaningfully step into Java runtime libraries.
There are a number of tools that come with the JDK that don't come with the JRE - JConsole (http://java.sun.com/developer/technicalArticles/J2SE/jconsole.html) springs to mind. This for example can help you understand & monitor the memory usage of your application and so on. Either way if you head into unfamiliar territory, I highly recommend you follow the Eclipse suggestion and use the JDK!
JDK is equipped with different helpful tools, as DotMasta mentioned. Eclipse's "version" of JDK is called JDT. Apart from range of shipped tools, there are also differences between javac and Eclipse built-in compiler ecj, so check here to see the comparison. One of the most important differences is that javac is strict, i.e. with ecj you can create a class file even in case of errors in code, which is perfectly suitable for testing phase, but not for launch :)
JDK contains software development tools which are used to compile and run the Java program.
Plenty of classes and methods in standard jdk library
Javac java compiler
Diffrences and why you will need this?
JDK includes the JVM, standard class libraries, and several other tools that a developer needs in order to create a Java program.
JRE includes the JVM, as the JRE provides some standard libraries and the JVM which can be used to execute a Java program.
You can even look there: http://en.wikipedia.org/wiki/Java_Development_Kit
I'm a little bit confused about the two different versions of Eclipse - 32/64bit.
As far as I know, Java bytecode (= build of your code) is platform independend. If a user runs your bytecode in a 32bit JRE, the code is executed in as a 32bit process, if a user runs your bytecode in a 64bit JRE, the code is exectued as a 64bit process.
Eclipse needs the JRE to run, cause it's written in Java. But why are there 32 and 64bit versions of Eclipse on the Eclipse download page if only the user's JRE version does matter?
Does a 64bit Eclipse version need a 64bit JRE or JDK? If yes ,why?
Second confusion: I understand the need for a 32 and 64 bit version of the JRE. But why are there 32 and 64 bit versions of the JDK if the resulting bytecode is platform independet?
Thank you
Eclipse relies on SWT, which is essentially native code. There will be quite a few DLLs etc. exists (in the plugins or features directories) that will be used by the 64-bit version, that are drastically different from the 32-bit version.
It is not because of the running environment, it is because Eclipse uses some native stuff and must be run on corresponding JDK. The applications you are developing inside Eclipse can then be run on whatever JRE you have installed, just specify it in the settings.
JDK is a compiler and also a lot of other stuff. Many of them are native applications that need to be run corresponding platform.
I have two JRE in my system. One is 32-bit and the other one 64-bit. In Eclipse I can configure both and choose which one to use when running my application.
I'm wondering if I can do the same thing in Netbeans. I've tried to go to Project Properties, Libraries and then tried to configure a new JRE there, through Manage Platforms, but it doesn't accept the directory of my JRE. How should I proceed?
Be aware that I'm talking about JRE, and not JDK ;)
EDIT: I managed to make it work by downloading a new 32-bit JDK and selecting its directory. I still couldn't make it accept a JRE directory.
Whether or not you can run Netbeans with just the JRE depends on what bundle you have downloaded. In Netbeans 7 only C/C++ and PHP bundles can be run with the JRE.
Older versions of Netbeans include more languages under this JRE umbrella, but the principle is the same.
The JDK contains the JRE plus tools to debug and compile code, so if you're doing anything Java based apart from just running the IDE, netbeans depends on the JDK.
To tell the truth, I am quite confused on all these terms (JDK/JRE/Java SDK). I am not sure what each one does.
When I first started doing simple java examples in eclipse, I am pretty sure I only had the JRE, which I believed was the default java installer regular users use to be able to run java programs/applets on their system.
However, now in class we are using Google Appengine, and this requires the JDK which I am guessing is the same as Java SDK. After wasting some time finding out that installing the JDK meant I also had to add java/bin to the environment variables to get javac -version to work in the command prompt I find that only the JDK has javac...
How were my early java programs working without having installed the JDK and therefore not having javac? And really the main question... What is the difference between the JRE and JDK, and when do you use each one?
Thank you :)
JRE = Java Runtime Environment - what you need to run programs/software that require Java or use libraries written in Java. For example, OpenOffice requires the Java Runtime Environment
JDK/Java SDK = Java Development Kit/Java Software Development Kit - what you need to write programs that require Java or use libraries written in Java. For example, if you were to write your own word-processing tool in Java.
java comes with the JRE because it launches the VM (virtual machine). It can take in class files which are files that have been compiled using the JDK.
The JDK comes with javac because that's what you need to compile your .java files into .class files that can then run on the JRE.
Eclipse has its own built-in compiler (called ecj), which is probably the reason you could get away with not having the JDK installed to use it. It does not use javac.
Google App Engine uses the javac that comes with the JDK.
What is the difference between the JRE and JDK and when do you use each one?
JRE: Java Runtime Environment. It is used to run Java programs only. As Chris Jester -Young mentioned, Eclipse had a built in compiler. That's why you just needed JRE ( to run eclipse )
If you ship a Java program, the only thing the client need to have is this runtime environment
JDK: Java Develpment Kit, this also includes a JRE inside, but additionally have other tools for program development such as the java compiler javac among many others.
If you want to create java program you should use this.
There's no way you used the JRE to compile Java programs. javac, the Java compiler, only comes with the JDK.
You may write Java programs with whatever text editor, you don't need anything special to do this.
You need the JRE to run Java programs. The JRE includes the Java Virtual Machine, needed to run already compiled Java programs.
You need the JDK to compile Java programs. So if you are a Java developer, you may want to only install the JDK since it comes with the tools needed to compile, in addition to the Java Virtual Machine.
'Sometimes you can develop with jre'
No. Never.
You develop with the Java Development Kit. You run with the Java Runtime Environment or Engine or whatever it's called.