teacher said: "your source code should compile in java “1.6.0”. This version is general. I search but cannot find the version.
Which version you think is better in this situation from following site:
http://www.oracle.com/technetwork/java/javase/downloads/java-archive-downloads-javase6-419409.html
How can we understand witch version of this site is almost the same version that we want
JDK 1.6 update 45 is the latest version for Java 6, so use that.
You don't really need to have exact version. Most of the code you write can be compiled in other version if you are just starting java programming, based on your question it seems you are just beginning.
There won't be too many changes among different updates of one version. So, you don't have to worry about it. If you want to be sure what ever you write can be compiled in 1.6.0, you can take any version of 1.5 and develop your code. This way your code will almost always compile in any version of 1.6. So, go ahead and use Java SE Development Kit 6u45.
Or if you want to just run already compiled code, it is enough if you take latest version of JRE.
When someone says 'your source code should compile in java “1.6.0”' they mean any Java 1.6.0 distribution.
All of the downloads on that page are for Java 1.6.0, so anyone of them will do. But with Java it is best to use the most recent patch release. This is currently Java 1.6.0 patch 45.
For the record, you are pretty much guaranteed that if your code will compile with one patch release of Java 1.6.0, it will compile with all of the. (As in, I am not aware of any case where this won't be true ... modulo the possibility of obscure compiler bugs in earlier patch releases.)
Related
My existing server is running on Java 1.6 and I cant upgrade it.
I need to use some third party jar/api that is compatible with Java 1.8, when I write some code to access its API, eclipse throws
Exception in thread "main" java.lang.UnsupportedClassVersionError: JVMCFRE003 bad major version
How I can proceed now? Not sure if this is duplicate question, if yes please provide some link on this.
The point is: Java virtual machines are not forward compatible.
A .class file that was generated by an "n+1" compiler can't be used on a "n" JVM. (unless you specifically instruct the compiler to compile for older versions of java)
Your choices:
see if you can acquire a version of that library compiled for Java 6
see if you can run your application on a Java 8 JRE (there is no problem running java6 classes on a newer JVM!)
Option 1 can get pretty ugly - as that library might have dependencies on system classes that Java6 doesn't have.
This is not possible to use multiples Java version or even multiples JVMs in the same project
If you really need this API, then you have just few choices, the best one is to upgrade all the project to use Java 1.8
No, you can't use jars compiled under java 1.8 in an environment running at java 1.6
As others have pointed out, you can't do this. However, you may be able to find older versions of the libraries you wish to use, and those libraries may support your particular version of Java. This potentially means that you will be adopting bugs into your software, but that's just how software evolves over time.
If you must use this 3rd party jar,
then you must compile the 3rd party jar using -target 1.6 (to target java 1.6).
Maybe you will get the source and compile it yourself or maybe you will get somebody else (the vendor, perhaps) to compile it.
All other options are:
Upgrade your JVM to Java 8.
Don't use that 3rd party jar. Either write or find one that is compatible with java 6.
Here is a small explanation of my problem.
I have an application which was compiled with java 1.5. This application is installed on 2000 pc (blockboxes) installed at customer premisses.
The jar of my application is often updated to add new feature and fixes, but for technical reasons, it is not very easy to update the java version, so I must keep using Java 1.5 on those existing machines.
Few months ago, I got a request for a new requirement for this application. To fulfil this task I have added the usage of Hazelcast in this application.
My problem if the following:
- Hazelacast jar file needs Java 1.6 or above, so I must compile my application with 1.6
- The new functionality using hazelcast will only be activated on demand by settings a new parameter. This means that it will not be used in the 2000 already installed blackboxes.
- All new blackboxes will be installed with Jave 1.6 or above to be able to use the Hazealcast functionality.
My problem is that I want to have a unique source code and unique version of my application for old blackboses using Java 1.5 and new blackboxes using 1.6 or above.
In the beginning, my idea was to always compile with version 1.5 and make sure that the new functionality would only be activated in blockboses using java 1.6 or above. This option is not working, because when I compile with 1.5, the compiler complains that Hazelcast jar file needs 1.6 :(
The second option would be to compile with 1.6, but then I cannot be sure that my application will still work properly on all blackboxes using 1.5. :(
I'm would like to know if someone here would know how to solve this kind of problem?
Just let me know if my explanation is not clear ;)
Thanks in advance for your help.
JVM is Backward compatible.You can run almost all code from Java 1 on Java 8.
So the best way is to use the option two. Compile it with 1.6 on some testing machines. And if it works( which most probably will) you don't have to make much change to the application .
You can compile your code to Java 1.5 bytecode using JDK 1.6, just take care of the following:
-source=1.5 and -target=1.5 compiler options
bootclasspath should point to rt.jar from JRE 1.5
See this post for more info: http://www.draconianoverlord.com/2014/04/01/jdk-compatibility.html
The post also recommends simply building your application with older JDK if possible. You need to figure out a different build process and exclude incompatible libraries from the classpath. If you use Maven, consider having two pom.xml files, with an optional parent file.
I am currently working on java 1.7 standard version, and I am really fun of the new features:
Nio(new input out put)
non redundant code with collections
...
I want to know if there is a way to switch the class I want to execute depending on the version of (JRE)java runtime environment it will be deployed.
You first need to create some sort of launcher app in order to check the JRE version of the environment, then you can lauch the JAR compiled for those version of the JRE. Your code cannot be compiled to newer versions of the JRE and be executed in an older one. That's why you need to complie the launcher app targeting a very old JRE.
As a side note, you can obtain the JRE version in which your program is running using:
System.getProperty("java.version")
The Java class file(s) are almost always binary compatible with new versions of the language (and the few exceptions, like using enum before the keyword was added, are fairly rare). If you restrict your usage of features to the "lowest common denominator" it is possible to compile back to an arbitrary version. That being said, Java 7 is now quite long in the tooth and I've found Java 8 to be remarkably stable. Finally, if you do choose to use new language features (like lambdas) you cannot use the earlier version of the language.
You can create two compiled build for both version to use language feature differently and have them running on jre 7, but you should just upgrade code compatibility and runtime to 1.8 (Even better)
I've read that the bytecodes that the JDK generate are generic. What I say is that they only do things like memory mapping, calling, etc... So if that's true, it would mean that I can, for example, if write a program with characteristics of JDK 1.7, I don't need to worry about if it can run in a user with JRE 1.6? (It's an example, it could happen with more exagerated cases).
So, my question is: Can I write a program with new things from 1.7 and run it in 1.6?
Can I write a program with new things from 1.7 and run it in 1.6?
No. Java is not backward compatible.
Note that it is possible to create code compatible with a Java 1.6 JRE in a 1.7 JDK by using the cross-compilation options, but that code can only use the classes, attributes, methods and language features available in version 1.6.
Can I write a program with new things from 1.7 and run it in 1.6?
The short answer is yes, but it is not officially supported. You'll have to resort to some hacks, but you can get it to work if you really want to. I wouldn't recommend doing this in a major project though.
In general bytecode is not backwards compatible because each classfile contains a version field. The JVM will refuse to run classes with a higher version than it was built for (lower versions are of course ok). By default, the javac that comes with Java 7 will create classes with version 51.0, which means they can only be executed by the JVM that comes with Java 7 or higher.
However, this doesn't mean it's impossible if you really want to create Java 6 compatible code. You can tell the compiler to generate classfiles with an earlier version. All this means is that you won't be able to use library and bytecode level features introduced in the new version.
Luckily, version 51.0 did not actually introduce any new bytecode features used by javac. All of the new features in Java 7 are implemented at compile time - the bytecode isn't any different except for the version! This means that any Java 7 class can be made to work as long as it doesn't rely on standard library updates (for example Try With Resources requires library support).
Unfortunately, javac refuses to compile Java 7 to version 50.0. But you can always change the bytecode version field yourself, either manually or with a tool. Since there were no new bytecode features, it will work just fine.
P.S. Memory mapping is down by the VM. There's no bytecode instructions for it. But you have the right idea.
I am looking for clarification in jdk versions.
I am getting error
java.lang.UnsupportedClassVersionError:Bad version number in .class file"
I hope this error is for different jdk version. I am having myeclipse6.0.1 and weblogic10.3.
Now, in my systems has jdk1.5 but weblogic has jdk1.6, as well myeclipse supporting 1.5 only.
I read the all forums and they said compile is different version and running different version.
So, here i thought program compliling 1.5 and running 1.6.
Is it correct ?
This means that the Java program was compiled for a newer version of Java than you are trying to run it with.
The easiest way to be certain is to use the same version of Java for compiling and building as is to be used on the final system. For you, this is most likely Java 5.