Migration of Java Application from 1.5 to 1.8 [closed] - java

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We are working in the project of migrating a application(built in java 5)
to java 8 for better performance,
But , we are not sure that
1. upgrade an environment or
2.Build that complete app in java 8 from scratch,
and how it will improve the performance !
And we know that, There will be some Deprecated API's from version to version.
so, while upgrading is it possible to get error or miss some functionality ?
How can We rectify that?
Please comment your suggestions !

Java has full backward compatability, So
If you just change java version then it will not have any errors as java8 is fully compatible with previous java versions.
If you want to improve performance using java8, Then you have to read java8 release notes to know where you can get faster alternative of current code and then you can only re-wright that functionality only

firstly you can always migrate to newer version of java as java is backward compatible. Also, you are right, few API's might have been deprecated but you always have the new options of those which can be solved.
My suggestion would be, if you don't have huge code or a bulky API, re-write the same in new version as u might utilize benefits of functional programming.

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How will Java 9 Jigsaw Affect Normal Maven/Gradle Java apps? [closed]

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I've read and performed all the exercises in the Jigsaw quickstart
I also notice that all my existing Maven/Gradle/SBT Java Projects seem to work as normal under Java 9 without any changes or benefits. Nothing is defining or using Java Jigsaw Modules.
Is the normal Java/JVM world of Maven/Gradle/SBT going to adopt Jigsaw in a more noticeable way? Are all the libraries and frameworks of the JVM world going to use Jigsaw? Is there a reason or benefit over the Maven-dependency system that exists today? Is there any point or benefit for normal Java developers to use Jigsaw at all?
EDIT: I've read several StackOverflow questions with these search terms and none of them addressed my question. The linked StackOverflow question is from well over a year ago about an error with Maven 3.3 against early builds of JDK 9. That is completely irrelevant. I'm not getting errors. Also, Maven 3.5 and the final JDK 9 are out at the time of this posting.

How java app for new version of windows will work on old version? [closed]

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So if I wrote an application for windows 8-10 on java, would it work for old versions like windows 98. And will it work correctly?
Both of them got the newest versions of JRE for example.
Well, you can't install Java 8 on systems older than Vista, so some programs might not run (specifically ones that use Java 8 features and APIs). Otherwise, they would work the same way, unless you do some sort of hacks that may break things.
If you had done your project in oldest version of java supported in vista/xp/windows 7 systems your application works perfectly it only depends on java environment once if it is satisfied your application will run without any compactability issues.

How to download JRE 1.8 for production environment? [closed]

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I'd like to use some Java8 features in my program. But I should deliver the program within 10 days and seeing that JRE 8 isn't available by oracle worries me. I see that Java8 features have been estabilished and looks to be very stable. My project is in the production camp and not for experiment.
When I search java runtime environment 8 or 1.8 I find nothing published by oracle. Am I making a mistake or I will have to install JDK8 for the client(The worst option). Or I should rewrite all the Java8 codes and make the software compatible with Java7.?
Is there another vendor who has the Java8 ready and if there is, is it wise to use their JRE in spite of the oracle one? Will it remain compatible?
Java 8 is not yet officially released, not from Oracle or any other vendor. There exists pre-release versions, but for a fully supported solution you have to wait until next year. You shouldn't depend on java 8 features yet for production quality code.
Update
Java 8 was fully released on 18 March 2014. It can be downloaded here (jre) or here (jdk).

New code on old JVM [closed]

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I have class corresponding with Java 1.5 and later. It's compiled in Java 1.7.
And now turns out that I have to launch it on Java 1.3.
How to solve that problem?
if you have the source files iwould just try to compile it in the version you need. if this won't work you need to "get rid of" unsupported stuff (e.g. generics)
if you don't have the source-files, i would trying to decompile it and compile it in the version you need.
Stackoverflow Answer on decompiling
You code in 1.5 and you compiled in Java 1.7(Java 7). if you want to run this one in to Java 1.3 then you need to sure about API what you used in code. The API what is used in code it should support in Java 1.3.
Example:-
Lets have a example. if you use generics in you code. but as we know java 1.3 not support generics. so this code not going to work on Java 1.3. you need to remove and look for alternative.
There are a few things to consider:
Class format (you can set the target class format to 1.3 even with 1.7 compiler)
API changes
Must not use generics
Ok, I solved it that way (quite primitive):
I compiled it using javac, then I opened it in Hex Editor, eight byte changed on 2F, saved and it works!

Java 7 / 8 in Android? [closed]

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Android is great mobile platform, it uses Java (for a good reason) a really popular programming language.
But the Java language is evolving, moving forward, the version 7 with small language improvements has some years and the next year it comes the version 8 with the awaited lambdas.
My question is: Will Android run Java 7 or 8 or take some of their constructs?
UPDATE: Just for non believers: In Android Kitkat 4.4 we can use Java 7 goodies: ARM, switch over strings, diamond,etc. Yeah!
I hope that it will not take so longer to get lambdas and Java 8 features
Android works today with Java 7, according to the tools team, though I have not tried it personally just yet. By this, I mean that you can compile an Android project with a Java 7 compiler, and the build tools will accept the Java 7 compiler output. AFAIK, there was only one new bytecode added (invokedynamic, or something like that), which is for interpreters, not the javac compiler.
Since Java 8 does not exist in final form, and since Google does not tend to give out future details like this (particularly given in-flight litigation), you will know when the rest of us know, sometime after Java 8 ships.

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