Sorry for the stupid question, I'm just beginning to learn Java. Can it be compiled into a .exe to be run on another computer, or is it only for computers with a JVM?
Not exactly. You can bundle a JRE with your executable, which is kind of like the same thing. Embedding a JRE is one approach offered by launch4j.
There are third party projects that will allow you to do this. A free one is http://gcc.gnu.org/java/ . I don't believe it's officially supported by Java though, but it's also gnu, who happen to know a thing or two about compilers.
There is also http://www.excelsior-usa.com/jet.html which is a paid product, but supports up to Java 6.
Can you make candy without sugar?
Yes, you need to have a JVM (just the executing for compiling) to run and to compile.
Although, it is not necessary when trying to write just the code.
Related
Nowadays, I've started hearing a lot about Java. I know that its because its meant to be cross platform. But is it really?
How much can we trust the client to have JVM installed? I've quite a few books on Java in my home and really wish to read them. But every time the same question strikes me. Will the apps which I develop with Java run on most of the machines? Isn't that bad?
One way out is to use some compilers to compile Java code to native machine code. But this makes me feel, "Why use Java then?"
So, Is it worth to learn Java for cross platform? Any ideas regarding the percentage of people having JVM installed?
I would like to correct you, People dont require jre installed they require jvm.
Since Java only relies on JVM, it is platform independent (if the platform has JVM installed).
But the main thing is, That the programmer do not have to know specific knowledge of the Platform and program his application keeping one specific platform in mind. He just has to write code generate byteCode and rest part is handled by JVM, to run it on any other platform.
If you compare java with other language you will get the exact difference like in In c/c++ the source code(c program file) after the compilation using a compiler is directly converted to native machine code(which is understandable to particular machine on which u compiling the code). And hence the compiled code of c/c++ can not run on different OS.
Nowadays, I've started hearing a lot about Java. I know that its because its meant to be cross platform. But is it really?
Yes, Java is cross-platform - or, more accurately, portable. It runs on the most used architectures and platforms, often without modification, which makes it one of the most portable languages out there. (But keep in mind that you can write unportable code in almost any language and Java is no exception.)
How much can we trust the client to have JRE installed?
We can't, but that's almost never problem.
Most languages need runtimes in order to operate. The C language (and some of its derivatives, like C++) get away with the fact that the C runtime is often already installed in the OS.
For most other languages, we trust the end user to be at least willing (not even necessarily able) to install the required runtime in order to run our (and others') software. Most software these days (and this often includes C++ software) installs its required dependencies automatically in the installation script. If this isn't desirable for any reason, an alternative is to bundle (statically link) the runtime with the program when deploying it.
One way out is to use some compilers to compile Java code to native machine code. But this makes me feel, "Why use Java then?"
Not all languages that compile to native code are the same. They have different features, different tools, different libraries available, and so on.
In any case, make sure you're not confusing native compilation with static linking of any dependencies (runtime or libraries).
Even, tell me how much percent people have a JRE installed.
About 97% of enterprise computers and 89% of desktops in the USA are estimated to run Java.
The client needs a JVM, not a JRE. They will run on almost all machines. I don't have a percentage but considering that pretty much every major OS has a JVM available to them, I would say around 95% (underestimation in my opinion). Java definitely does not have a limited audience so that shouldn't stop you from using Java.
Updated in light of Andreas' comment. I was under the impression that a lot of machines came pre-installed with Java. However, the JVM can be easily downloaded so you still don't have to worry too much about whether you're going to miss out on a large audience.
I think you mixed two different concepts:
Cross-platform: A program is considered to be cross-platform if it can run on different platforms without a need to recompile it.
Q: Is Java cross-platform?
A: Of course it is.
Native app: A program that runs on the targeted platform without a need to install, download any other software. Usually the program is compiled into a machine binary. However, it may in some definitions include programs/scripts that are not machine binaries, but the target it platform is guaranteed to run them with its built-in library/software.
Q: Can Java run on any platform without JVM?
A: No. JVM is not shipped with any platform that I'm aware of, so it needs to be downloaded and installed before any Java program can run.
One way out is to use some compilers to compile Java code to native machine code. But this makes me feel, "Why use Java then?"
It all depends on what you want to achieve. If you want to create native apps, drivers, etc, then Java is definitely the wrong tool. But if you want to create an app that can run on all platform without having to recompile it and create a version for each platform, then Java can be a good option.
So, Is it worth to learn Java for cross platform? Any ideas regarding the percentage of people having JVM installed?
Again, it really depends on what you want to achieve. Java is a good option for creating cross-platform apps and it is worth learning. However, there are other options that you may want to look into, compare, and decide which one to learn. C# is a great language, and just recently, Microsoft announced its plans to make it truly cross-platform, so it is another good option.
Most PCs have JVM installed. Theodoros Chatzigiannakis provided some statistics in his answer. But you shouldn't be too worried about the numbers. Those few who don't have JVM installed, will be willing to download and install it if they like your app.
Note: In the past, you could run apps written in C# on platforms other than Windows, but you needed a .Net Framework equivalent (e.g. Mono). With Microsoft recent announcement, we should be able to use Microsoft .Net Framework itself on other platforms. We will see how this will turn out.
How does one start a Java VM from C? Writing the C code seems to be straigtforward -- I've been following the code that appears on p. 84 of Liang's "The Java Native Interface". It's the linking process that has me stymied. Liang's book is 10+ years out of date in that regard and I can't find anything on the net which addresses this goal (and which works).
To be clear, what I want to do is launch a standard windows program (written in C), which then launches the JVM and calls a main() in a Java class (which I have written). This program should not rely the presence of jvm.dll or jvm.lib -- the user shouldn't have to install Java to run the program. Maybe this isn't possible without an unreasonable amount of effort.
The development environment is MinGW under windows. I'm able to link in such a way that the program works when the .dll is in a separate file, but not in a way so that there's only a single executable without any .dlls or .libs.
In hindsight, I can see now that this was a dumb question, or at least one that hadn't been thought through. The moral of the story is that the "JVM" is not a single executable, or even an executable plus some JAR files; the JVM relies on a slew of independently stored files with various mutual dependencies. Unraveling all of these relationships so that they could be brought into a single file (or even two files) would be a massive undertaking. Thanks for the knock in the head.
So, to be clear - you want to launch a JVM without the requirement of a JVM being present? How do you propose to accomplish that? Unless you're contemplating writing your own JVM implementation (which I'd say falls under the category "unreasonable amount of effort"), having a JVM installed is a reasonable requirement. Assuming that, you can just spawn a java process and include the appropriate command-line parameters (classpath, class to run etc).
Disclaimer: I don't think that having a Java runtime installed is unreasonable for users. That said, I do understand your motivations for a low-friction install for users.
Using the Sun JRE is probably not going to be fruitful here. In theory, you could grab the Sun JRE, modify it to build as a static library instead of a DLL and figure out a way to cram all the resources that get bundled with it (fonts, images, cursors, SSL certificates, localized message files, etc.) into a single resource and then modify the runtime to load from there. But this is almost certainly an "unreasonable amount of effort."
You might want to look at GCJ instead: its architecture is different than the Sun JRE which lends itself more to being embedded in another application, or it can compile your Java to native machine code.
(Also, do check the licensing to ensure that you can properly redistribute this no matter which route you take.)
when you write an app in java, people need to have this java installed to use it right?
Sorry if this is a dumb question.
Traroth is correct; your audience needs the Java Runtime in order to use your java.
However, they don't necessarily need that Java, or in other words, they don't need to be using Sun (now Oracle)'s JRE. They could also be using the OpenJDK, or any of the other free java implementations.
Not a silly question at all.
Side Note: As Glenn Nelson stated, there are Ahead-Of-Time compilers, and if you want to go down that route, go ahead. But I'd strongly warn against jumping into that boat, especially if you are just starting off in Java. AOT Java compilers come with their own set of issues.
Yes, you need the Java Runtime to run a java program:
http://java.com/en/download/
There are also executable installers which may bundle Java or download it during the installation. You may also use "Java Web Start".
Want to create animation dll for Window XP
Is it ok to create Java2d animation and export as dll??
Yes. You need to write code in C++ to start the JVM with the invocation interface to JNI, and call into it. However, you may find it difficult to create windows in this way that integrate seamlessly with your Windows environment application to display your animation. This is a rather advanced JNI usage, and I'd recommend reading the JNI book before even trying a little bit of it.
I am pretty sure you can only create .Jar files from java not dlls
I doubt so, unless there's some 3rd party tools out there. For your case where graphics is involved, chances are even lower.
Actually, what Quentin said should work. When you compile java to native with GCJ you first compile the .java files into platform specific .o (object) files. Presumably you would compile the .o files into a dll rather than an exe. GCJ also includes components like the garbage collector, and base java libraries. None of which require a JVM to run. The downer is that the dll would be huge. A simple "Hello World" app when compiled with GCJ is ~35MB, thanks to all the default libs and the garbage collector. Likewise your dll would be huge.
There are "bridges" that allow Java and non-Java code to call into one another. Depending on what you are trying to accomplish, these might be useful as you could write your Java code and then call into it from a C++ or C# DLL, depending on which language you are creating your DLL with, which will also determine what kind of bridge you need. I have never seen a freely provided bridge though. All the ones I've found when looking had to be purchased.
No, IIRC you can't. DLLs are linked directly when loaded. Java code needs a jvm, so you can only provide a dll that starts a jvm and starts code there, but not all necessarily stuff fits in the dll.
You should not do this. It looks like you're trying to use the wrong approach for your problem.
Well…
GCJ is available for Windows.
GCJ is part of GCC.
GCC can create dlls.
It might be possible to put that together to build DLLs using GCJ.
Yes, it is possible to generate DLLs from Java source code.
2 Methods I have used:
IKVM
Graal
IKVM is mature, but rather slow in runtime execution of the generated DLL.
Graal is fast, but early days and immature in the Windows environment.
See https://openjdk.java.net/jeps/295 for further info.
There are other commercial options available as well.
I agree with bmargulies. It's probably feasible for an expert, but it would be a large DLL and you'd be mixing technologies that were never made to work together. It doesn't make sense to try this, in my opinion.
I've been charged with creating a little GUI launcher app to go on a CD which will offer the user some software and some videos. It's not being aimed at particularly tech-savvy people, so it needs to be quite simple. I guess the real sticking point here is that it will be form based.
I would very much like the launcher to just run from an exe without having to install any .net stuff or have java installed. I know ClickOnce is fairly simple and I will fall back on it if necessary, but I thought it might be worth asking if there are any easy ways to do this.
I mainly program using visual c# these days, but have experience with java and c and I am a relatively quick learner, so feel free to suggest other languages.
The most straightforward way to create a dependency-free executable for Windows is to use ordinary Win32 functions from C (or C++). Alternatively, you could use MFC with C++ because you can link MFC right into your executable to avoid a dependency on MFC DLLs.
There are probably other C/C++ frameworks that can be linked into an executable. However, you probably want to avoid Java and C# or any other .Net language, if you want minimal dependencies.
Depending on the minimum target OS, you could possibly choose VB6, if it doesn't affend you too much, because the VB6 runtime has been included in windows since Windows 2000. However, you need to stick to the included controls to keep things simple.
If you write it in Java you could bundle the JRE on the CD and just have a batch file that uses that bundled JRE to launch the app. This should work, but the JRE is kind of large, so you'd need to make sure you'll have enough space on the CD for it.
.Net might be able to do something similar but I've never looked into it at all.
The simplest thing would probably be to just write a simple native app in C/C++ (or in some other language that compiles to a standalone EXE) and use that.
Just statically link to the C runtime library and any others you might need (like MFC): /MT or /MTd on the command line and Project Properties > C/C++ > Code Generation > Runtime Libraries in Visual Studio.
You can use C++ with wxwidgets for GUI and statically link your application
Now all the windows OS (from win 2003) pre installed with .Net frameworks... so you can go ahead and code in any CLR language...
You are saying ur clienats are not tech ppl, so the chances for uninstalling .net frameworks from their machine is very low..