How does Java differ on different platforms?

Question

I am currently in high school. I was recently browsing the internet looking for what employees in the software industry usually want and what the job requirements are like.

I came accros a job description and one of the requirement is:

Strong, object-oriented design and coding skills (C/C++ and/or Java preferably on a UNIX or Linux platform)

Note the last part: Java preferably on a UNIX or Linux platform .

I don't understand this. Isn't Java run inside a virtual environment/machine? Why would it matter what OS it is running on since Java cannot directly interact with the OS?

Answer 1

A developer job description may require experience with some OS for several reasons:

1. First, as you noticed already, there are languages that talk directly to the OS and the code needs to be aware of the underlying OS (like C/C++, which are listed in your job description).

2. Secondly, even if the programming language abstracts away anything that's OS-specific from you (including the file-system / path separators), you are still going to deploy / configure / run / monitor your applications on top of some OS and you need to know (at least) the basics in order to do that.

For a Java job description, If UNIX/Linux "is a plus", it usually means you're going to run your code on a UNIX/Linux system and you should know how to start a process (your own java app or some application server), how to deploy an application in a container, how to read log files and so on...

Answer 2

While Java the language runs on a virtual machine , the Java library must abstract access to facilities available on the host platform. Ideally, these abstractions are cross-platform, but the devil is in the details—hence the preference for experience on a particular target platform.

Answer 3

Develop once debug everywhere

While conceptually it shouldn't make any difference on what target platform the java code is executed on unfortunately in practice it isn't always that simple but a rather tedious task to get the code running on any platform.

Beginning from easy to circumvent mistakes eg using / or \\ instead of java.io.File.separatorChar or : / ; instead of or java.io.File.pathSeparatorChar there are most often problems including methods implemented in native code that often aren't that compatible across different platforms.

It might be even possible your employer is looking for someone to implement native java methods using JNI.

Answer 4

First, you're right in that Java runs inside of a virtual machine - it doesn't directly expose the inner workings of the system to you. However, that doesn't mean that each system doesn't differ in some way under the covers - different flavors of operating systems have different kernels, different ways they think about scheduling, different ways to handle threading, and different interrupt chains (Linux has quite a few signals, whereas Windows has a handful).

As far as Java (the language) is concerned, it runs the same everywhere. How it's actually accomplished is dependent on the native JVM that it's running on.

For this job posting, though, I wouldn't read too much into the UNIX/Linux portion. This is more or less gauging how comfortable someone would be working in a UNIX or Linux environment while programming Java. The majority of IDEs available for Java are cross-platform, but that shop may be using Mac or some flavor of *nix (RHEL, Debian, Ubuntu, etc). It'd also be important to make use of the command line/shell script, since a lot of the convenience of working with UNIX/Linux is on the command line.

Not every shop uses Windows machines to develop on. Just a heads-up.

Answer 5

Java does not differ on different platforms. That is the most highlighting feature of Java ( portability ). The JVM abstracts the underlying platform.

However, platform matters when it comes to a software development, which involves not just the coding part. Mostly in industries, devs work on Linux platform by logging into a terminal. You don't get a GUI as in Windows and a good IDE like NetBeans. So in that case, you should know how to compile and run a java program from terminal.

Example, In linux, In order to create a package, you create a directory ( folder ), say myJava/. You go into it (cd myJava) and write the SomeThing.java file and compile using javac SomeThing.java and you get a SomeThing.class file ( inside myJava ). Now in order to execute this, you need to use the java command. Prior using it, you need to move to the parent directory containing this package. Then execute as java myJava.SomeThing . You wouldn't be knowing this unless you play around in Linux platform. Other things like setting up the classpath etc are also matters of concern