newbie to java

[javaalien]

I have couple of questions about java, can anyone here help me knowing basic things about the language:

1.Which java version that I have to download? When I checked the java sun website, there are J2SE v x, Java EE x SDK and J2RE…Could anyone please tell me which one to download to do programming and what are there others for?
2.I don’t get what is java library here? Is that compilation of all the java core classes that we need to set in classpath?
3.What is Java documentation? Where to install it?
4.Why I/O classes are called native method / platform specific in java?

Your help is very much appreciated….Thank you in advance.

[JosAH]

I have couple of questions about java, can anyone here help me knowing basic things about the language:

1.Which java version that I have to download? When I checked the java sun website, there are J2SE v x, Java EE x SDK and J2RE…Could anyone please tell me which one to download to do programming and what are there others for?
2.I don’t get what is java library here? Is that compilation of all the java core classes that we need to set in classpath?
3.What is Java documentation? Where to install it?
4.Why I/O classes are called native method / platform specific in java?

Your help is very much appreciated….Thank you in advance.

The latest version of Java is 1.6. You need to download the Java JDK which
stands for Java Development Kit. It contains the compiler and other tools.
The JDK has a JRE bundled in its download package (Java Runtime Environment)
which you need for actually running your compiled classes. When you install
the JDK you automagically install the JRE that comes with it.

The Java library is the set of all the classes that come with the JRE. If you
download the entire JDK you also get all the source files for those classes.

The Javadocs are very handy; install them anywhere you like and bookmark
the main entry point of those html documentation files in your browser. You'll
need that documentation over and over again.

IO classes need a couple of native (machine code) classes to do their work.
Every OS treats IO differently so a bit of machine code is necessary. You, as
a Java programmer, won't need those native classes directly, i.e. you just 'talk'
to the Java classes that implement all the IO for you.

kind regards,

Jos

[javaalien]

The latest version of Java is 1.6. You need to download the Java JDK which
stands for Java Development Kit. It contains the compiler and other tools.
The JDK has a JRE bundled in its download package (Java Runtime Environment)
which you need for actually running your compiled classes. When you install
the JDK you automagically install the JRE that comes with it.

The Java library is the set of all the classes that come with the JRE. If you
download the entire JDK you also get all the source files for those classes.

The Javadocs are very handy; install them anywhere you like and bookmark
the main entry point of those html documentation files in your browser. You'll
need that documentation over and over again.

IO classes need a couple of native (machine code) classes to do their work.
Every OS treats IO differently so a bit of machine code is necessary. You, as
a Java programmer, won't need those native classes directly, i.e. you just 'talk'
to the Java classes that implement all the IO for you.

kind regards,

Jos

Thank you for the brief explanation.
I don't get the native codes part. What do you mean by couple of native classes? Do you have an example about it?
Appreciate your help ...

regards,
alien

[JosAH]

Thank you for the brief explanation.
I don't get the native codes part. What do you mean by couple of native classes? Do you have an example about it?
Appreciate your help ...

regards,
alien

Java classes can have native methods. e.g. the following class has two native
methods:

public class Foo {
   static {
      System.loadLibrary("YourLibWithBarAndBazInIt.dll");
   }
   public static native int bar();
   ...
   public native baz();
}

This tells the compiler that the methods bar() and baz() are written in C or C++.
The static initialization code loads a dll that contains those functions.
Whenever another piece of Java code invokes either bar() or baz() the JVM
'knows that it has to call a function written in C or C++.

Before you can write those function you have to generate a .h header file that
properly declares those functions. The "jnih" tool is used for that. Pass it the
Foo.java source file and jnih generates a .h file for you in which the prototypes
of bar() and baz() are stored. The names are rather mangled (try to generate
such a .h file and see for yourself). You have to implement function having those
names and wrap the compiled code up in a .dll file.

If you're just starting to use Java the entire JNI (Java Native Interface) can be
skipped for now. As a matter of fact there exist quite a few experienced Java
programmers who never used JNI at all.

kind regards,

Jos

[javaalien]

Java classes can have native methods. e.g. the following class has two native
methods:

public class Foo {
   static {
      System.loadLibrary("YourLibWithBarAndBazInIt.dll");
   }
   public static native int bar();
   ...
   public native baz();
}

This tells the compiler that the methods bar() and baz() are written in C or C++.
The static initialization code loads a dll that contains those functions.
Whenever another piece of Java code invokes either bar() or baz() the JVM
'knows that it has to call a function written in C or C++.

Before you can write those function you have to generate a .h header file that
properly declares those functions. The "jnih" tool is used for that. Pass it the
Foo.java source file and jnih generates a .h file for you in which the prototypes
of bar() and baz() are stored. The names are rather mangled (try to generate
such a .h file and see for yourself). You have to implement function having those
names and wrap the compiled code up in a .dll file.

If you're just starting to use Java the entire JNI (Java Native Interface) can be
skipped for now. As a matter of fact there exist quite a few experienced Java
programmers who never used JNI at all.

kind regards,

Jos

Oo really! sounds relief then.
btw, from the example's given that's clearly shows that the java class calls native method. How about the i/o operations that said to be native to java?
Please share some examples to me. thank you again.

[JosAH]

Oo really! sounds relief then.
btw, from the example's given that's clearly shows that the java class calls native method. How about the i/o operations that said to be native to java?
Please share some examples to me. thank you again.

All Java IO that deals with physical IO (think of files, sockets, terminal IO etc.)
has to have at least one native member method that deals with the nitty gritty
platform dependent details. The details are neatly hidden from you, i.e. you
only have to deal with the Java classes.

kind regards,

Jos