System Class In Java

Hi,
From the Sun Java Docs,I have seen that the System class is a public final class.But it stated in the docs that the class cannot be instantiated. A class cannot be instantiated only when it is an abstract one or it is an interface.Can any one tell me the reason??

There are other ways to make a class non-instantiable. Making the constructor private is the (first) and only one that comes to mind. Maybe someone else can list other ways.

Similar Messages

ERROR: Unable to locate system class: java/lang/String

I have swtiched from running my application using sun jvm to using microsoft jvm. When i run it i get the following error:
ERROR: Unable to locate system class: java/lang/String
java -classpath out;etc..etc myclass
has become
jview -cp:a out;C:\build\rt.jar;etc..etc myclass
any ideas?

Search for the old "MS SDK for Java 4.0" somewhere (no, you can't find it at Microsoft's site).
There are two files that you have to get: sdkdocs40.exe (a file with 10,895,496 bytes) and SDKJava40.exe (a file with 20,222,928 bytes).
Use the embedded jvc compiler to recompile your program. Beware: try not to rely too much in jvc. Use it only for discover that you're using methods not implemented in JDK 1.1.8, but don't use it for deploying your app.
You'll discover that you'll have to rewrite large portions of your program, and even change your program specifications to deal with the reduced functionality of the old MS JVM (for instance, say that you'll need to change the 'modified date' of a file.
In JDK >= 1.2 there's the method File.setModified(); in MS JVM you'll need to use some com.ms.wfc function.

ORA-29547: Java system class not available: oracle/aurora/rdbms/Compiler

Hi experts,
I get the above error when I run the following code using sqlplus:
create or replace and compile java source named "DirList"
2      as
3      import java.io.*;
4      import java.sql.*;
5
6      public class DirList
7      {
8      public static void getList(String directory)
9                        throws SQLException
10      {
11         String element;
12
13
14         File path = new File(directory);
15         File[] FileList = path.listFiles();
16         String TheFile;
17         Date ModiDate;
18         #sql { DELETE FROM DIR_LIST};
19
20         for(int i = 0; i < FileList.length; i++)
21         {
22             TheFile = FileList[ i ].getAbsolutePath();
23             ModiDate = new Date(FileList[ i ].lastModified());
24
25             #sql { INSERT INTO DIR_LIST (FILENAME,LASTMODIFIED)
26                    VALUES (:TheFile,:ModiDate) };
27         }
28     }
29    }
30 /
create or replace and compile java source named "DirList"
ERROR at line 1:
ORA-29547: Java system class not available: oracle/aurora/rdbms/CompilerAny body can tell me what to do to run external commands like os commands using pl/sql in details with example.
I will appreciate any sooner response.
Thanks

What is the output of this query?
SQL> select owner, object_name, object_type from dba_objects where object_name = 'oracle/aurora/rdbms/Compiler' ;
OWNER                          OBJECT_NAME                     OBJECT_TYPE
SYS                            oracle/aurora/rdbms/Compiler    JAVA CLASS
PUBLIC                         oracle/aurora/rdbms/Compiler    SYNONYM
2 rows selected.
SQL> disconnect
Disconnected from Oracle9i Enterprise Edition Release 9.2.0.3.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.3.0 - Production
SQL>

How to load a class dynamically in the current/system class loader

I need to dynamically load a new jdbc driver jar to the current/system class loader... Please note that creating a new classloader will not help since the DriverManager refers to the systemclassloader itself.
Restarting the application by appending the jar to its classpath will solve the problem but I want to avoid doing this.

Did you then create a ClassLoader to load the JDBC
driver and then install it into the system as
directed by the JDBC specification (ie
Class.forName(someClassName))?
And then try to use it from a class loaded fromsome
other ClassLoader (i.e. the system class loader)?
If you did not try this please explain why not.O.K. I just looked at the source to
java.sql.DriverManager. I did not know what I was
talking about, as what I suggested above will not
work.
This is my new Idea:
Create a URLClassLoader to load the JDBC driver also
in this ClassLoader you need to place a helper class
that does the following:
public class Helper {
public Driver getJDBCDriver(String driverClassName,
String url) {
try {
Class.forName(driverClassName);
Driver d = DriverManager.getDriver(url);
return d;
catch(Exception ex) {
ex.printStackTrace();
return null;
}Now create an instance of the Helper class in the new
ClassLoader, and call its getJDBCDriver method to get
an instance of the driver (you will probably have to
create an interface in the root class loader that the
Helper implements so that you can easily call it).
Now from the root classloader you can make calls
directly to the returned Driver and bypass the
DriverManager and its restrictions on cross
ClassLoader access.
The only catch here is that you would have to call to
the returned Driver directly and not use the Driver
Manager.This sounds like will work but I did not want to load DriverManager in a new classloader.. I did a hack
I unzip the jar dynamically in a previously known location (which I included in my classpath when launching the app). The classLoader finds the class now though it did not exist when the app was launched !
A hack of-course but works eh ..

Using List Class in java.awt / java.util ?

have a program that:
import java.util.*;
List list = new LinkedList();
list = new ArrayList();
... read a file and add elements to array
use a static setter
StaticGettersSetters.setArray(list);
next program:
import java.awt.*;
public static java.util.List queryArray =
StaticGettersSetters.getArray();
If I don't define queryArray with the package and class, the compiler
gives an error that the List class in java.awt is invalid for queryArray.
If I import the util package, import java.util.*; , the compiler
gives an error that the list class is ambiguous.
Question:
If you using a class that exists in multiple packages, is the above declaration of queryArray the only way to declare it ?
Just curious...
Thanks for your help,
YAM-SSM

So what you have to do is explicitly tell the compiler which one you really want by spelling out the fully-resolved class name:
import java.awt.*;
import java.sql.*;
import java.util.*;
public class ClashTest
    public static void main(String [] args)
        java.util.Date today    = new java.util.Date();
        java.util.List argsList = Arrays.asList(args);
        System.out.println(today);
        System.out.println(argsList);
}No problems here. - MOD

Making system calls in java

I want to join some split files into one. In command prompt I use COPY /B file.1+file.2 file to join the files. How can i do the same in my java application. Please show the code which I suppose will use getRuntime. Thanks in advance.

Well if there is a problem with system calls then can
you tell me if there is a class in java for
concetanating files. Not directly.
At present I am joing the files
by reading each byte from the files and writing them
to another file which takes hell lot of time. You should read the files in large chunks. Much much faster.
Thanks
in advance again. Also if you say about sequential
file class then please expalin a bit bcs I couldn't
implement it.Post the code you are having trouble with explaining what it should do and what it actually does.

Using ExecutorService class from java.util.concurrent package

Dear java programmers,
I have a question regarding the ExecutorService class from java.util.concurrent package.
I want to parse hundreds of files and for this purpose I'm implementing a thread pool. The way I use the ExecutorService class is summarized below:
ExecutorService executor = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 1000; i++){
            System.out.println("Parsing file No "+i);
            executor.submit(new Dock(i));
        executor.shutdown();
        try {
            executor.awaitTermination(30, TimeUnit.SECONDS);
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        executor.shutdownNow();However, the code snippet above creates all the 1000 threads (Dock objects) at once and loads them to the executor, and thus I'm worrying about memory leak. I haven't tested it on 1000 files yet but just on 50 small ones, and even if the program prints out "Parsing file No "+i 50 times at once, it executes normally the threads in the background.
I guess the write way would be to keep the number of active/idle threads in the executor constant (lets say 20 if the thread pool's size is 10) and submit a new one whenever a thread has been finished or terminated. But for this to happen the program should be notified someway whenever a thread is done. Can anybody help me do that?
thanks in advance,
Tom

Ok I found a feasible solution myself although I'm not sure if this is the optimum.
Here's what I did:
        ExecutorService executor = Executors.newFixedThreadPool(10);
        Future<String> future0, future1, future2, future3, future4, future5, future6, future7, future8, future9;
        Future[] futureArray = {future0 = null, future1 = null, future2 = null, future3 = null, future4 = null, future5 = null,
        future6 = null, future7 = null, future8 = null, future9 = null};
        for (int i = 0; i < 10; i++){
            futureArray[i] = executor.submit(new Dock(i));
        }I created the ExecutorService object which encapsulates the thread pool and then created 10 Future objects (java.util.concurrent.Future) and added them into an Array.
For java.util.concurrent.Future and Callable Interface usage refer to:
[http://www.swingwiki.org/best:use_worker_thread_for_long_operations]
[http://www.particle.kth.se/~lindsey/JavaCourse/Book/Part1/Java/Chapter10/concurrencyTools.html]
I used a Future[] Array to make the code neater. So after that I submitted -and in this way filled up- the first 10 threads to the thread pool.
        int i = 9;
        while (i < 1000){
            for (int j = 0; j < 10; j++){
                if (futureArray[j].isDone() && i < 999){
                    try{
                        i++;
                        futureArray[j] = executor.submit(new Dock(i));
                    } catch (ExecutionException ex) {
                        ex.printStackTrace();
                    } catch (InterruptedException ex) {
                        ex.printStackTrace();
            try {
                Thread.sleep(100); // wait a while
            } catch(InterruptedException iex) { /* ignore */ }
        executor.shutdown();
        try {
            executor.awaitTermination(60, TimeUnit.SECONDS);
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        executor.shutdownNow();
    }Each of the future[0-9] objects represents a thread in the thread pool. So essentially I'm check which of these 10 threads has been finished (using the java.util.concurrent.Future.isDone() method) and if yes I replenish that empty future[0-9] object with a new one.

System class loader vs application class loader

Hello
I have a class that uses a third partyjar which I have put in /jre/lit/ext. The class compiles but fails at runtime being unable to read the property files called in the class' constructor. I believe that is b/c the third party jars are loading w/ the system class loader and cannot "see" the property files "floating" at the same level as the class that is calling them.
So I created a jar, of the property files, with the same directory/package structure as the location of the property files and put that in the /jre/lib/ext and STILL the same problem; cannot read the property files, the constructor fails, fugly. There is an overloaded constructor that includes a parameter for the property files, but I need to get this to work as is first. What am I missing? Please edify me. tia.

If the 3rd party jar needs a certain properties file to initialize correctly, I doubt it would be looking for it in the class hierarchy. I mean I doubt it does:
Properties p = new Properties();
p.load( getClass().getResourceAsStream() );It's more likely to do:
Properties p = new Properties();
p.load( new FileInputStream(...) );The reason is that the property file should be easily edited by the user and users know how to move around in the file system, not in the Java jars and classpaths.
Just a guess...

Only one business system for outbound java proxies?

Hi!
I have a problem regarding java proxy runtime JPR.
When I call the deployed outbound proxy from a client program, the java proxy sender service is always one defined business system. even if that has nothing to do with the business systems used by the proxy.
For example: I define a business system on the Web AS, which is responsible for the java proxy communication, this is the bean defacto. When I call this bean from a client the JPR calls the Integration Server using another business systems channel. Of course I get the runtime exception service unavailable, because it is not used in interface determination, as the sending channel. If I use the 'working' business systems channel it works just fine
I hope you get my problem.
If I enter the Adapter Monitor, then choose the JPR I can see under Cache that the working business system has several entries here.
Where is the difference between the one working system and others, has anybody ever faced this problem?
regards
Stefan

When you call an outbound java proxy bean, the sender business system is usually derived from the business system which is connected to the technical system Web AS Java in SLD.
If you want another sender business system, then you can set this with the application program with help of the message specifier class (look at manual for further details).
I recommend writing a wrapper bean around the generated proxy bean classes to enable the sending application program to provide the business system as a parameter. In that way different senders can provide their business system separately.
Regards
Stefan

System memory in java.

Anyone knows how to detect how much memory is still available in the system by using java? I got java.lang.OutOfMemoryError exception. so want to know if there is a way to find out the memory of the system.
Thanks!

Hello,
There are two methods for getting the memory details of the system on which the JVM is running. These are:
Runtime.freeMemory( )and,
Runtime.totalMemory( )These methods are stored in the Runtime class which is located in the java.lang package.
The values returned ( bytes) by these methods are an approxomation, "but are perfectly acceptable".
I hope this helps,
-Marek.

How to read system eventlog using java program in windows?

How to read system eventlog using java program in windows?
is there any java class available to do this ? or any one having sample code for this?
Your friend Zoe

Hi,
There is no java class for reading event log in windows, so we can do one thing we can use windows system 32 VBS script to read the system log .
The output of this command can be read using java program....
we can use java exec for executing this system32 vbs script.
use the below program and pass the command "eventquery"
plz refer cscript,wscript
import java.io.*;
public class CmdExec {
public static void main(String argv[]) {
try {
String line;
Process p = Runtime.getRuntime().exec("Command");
BufferedReader input =
new BufferedReader
(new InputStreamReader(p.getInputStream()));
while ((line = input.readLine()) != null) {
System.out.println(line);
input.close();
catch (Exception err) {
err.printStackTrace();
This sample program will list all the system log information....
Zoe

How to read system evenlog using java program in windows

How to read system evenlog using java program in windows???
is there any java class available to do this ? or any one having sample code for this?
Your friend Zoe

Welcome to the Sun forums.
>
How to read system evenlog using java program in windows???>
JNI. (No.)
>
is there any java class available to do this ? or any one having sample code for this?>You will generally get better help around here if you read the documentation, try some sample code and come back with a specific question (hopefully with an SSCCE included).
>
Your friend Zoe>(raised eyebrow) Thank you for sharing that with us.
Note also that one '?' denotes a question, while 2 or more generally denotes a dweeb.

Set system classpath using java program??

Hi,
I want to set the System classpath using java program. Can somebody please tell how to do this.
Prashant

but this will set the classpath for that particular JVM only.
Isn't it??? I want that of SYSTEM so that user can access that class path from any JVM instance.
Prashant

System Call by Java Application - [change path and run of the other progra]

public class A {
     public static void main (String[] args)
          System.out.println("Hi");
}I do have above A.java.
I am generating A.class from it.
A.class is in the following directory :
/home/sachin/work/Sample_Directory/bin/hello_filetest/
I have another program which makes System call.
But the problem is B.java is in the different directory :
/home/sachin/work/Sample_Directory/src/hello_filetest/
public class B {
     public static void main (String[] args) {
Process p1 = Runtime.getRuntime().exec("java A);
            BufferedReader stdInput = new BufferedReader(new
                 InputStreamReader(p1.getInputStream()));
while ((s = stdInput.readLine()) != null) {
                System.out.println(s);
{code}
        So, my question is how to change directory by system calls and execute the program
which is lying in other directory ????
Thank you.

The following code will call javac on a .java file, which will compile it into a .class file
     public static void javacTest() {
          JFileChooser jf = new JFileChooser();
          if (jf.showOpenDialog(null) != jf.APPROVE_OPTION) return;
          File file = jf.getSelectedFile();
          File dir = file.getParentFile();
          try {
               Process p = Runtime.getRuntime().exec("javac " + file.getName(), null, dir);
               IOUtils.pipe(p.getInputStream(), System.out);
               IOUtils.pipe(p.getErrorStream(), System.out);
          catch (IOException iox) {
               iox.printStackTrace();
     }Is that what you're trying to do, or are you trying to run the compiled (.class) file? Running your .class file should be basically the same as the above, assuming that you are not using any non j2se libraries, except that you need to take into account the package (if package is x.y, you must have file in ...src\x\y\foo.class - call "java x.y.foo" from src)

How to get system tasks using Java?

I have question about system tasks. I have to list all tasks which are working in the system. Is there any class which i useful to do that? I've tried to write shell script but it won't be working in system different than Linux. I will be grateful for any help.

In the standard Java classes, there are no such implementation. You are sort of answering the question youself, since you've made a script to do it. It is the same for all systems. To get the system information you need to talk to the system and to do that you need to know what system you are on...
Some system functions are more or less the same in all systems so they can be reached by the Systems-class.

System Class In Java

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