// __
[root@localhost XSD02]# javac javac02.java
javac02.java:33: illegal escape character
 aCmmnd = new String[]{"echo","\$PATH"};

// __ 1. java reachable from within my box' PATH

[root@localhost XSD02]# echo $PATH
/usr/kerberos/sbin:
/usr/kerberos/bin:
/usr/local/sbin:
/usr/local/bin:
/sbin:/bin:
/usr/sbin:
/usr/bin:
/usr/X11R6/bin:
/opt/jdk/jdk1.5.0_03/bin:
/usr/local/jwsdp-1_6/jaxb/bin:
/usr/local/ant/apache-ant-1.6.5/bin:
/root/bin

[root@localhost bin]# pwd
/opt/jdk/jdk1.5.0_03/bin
[root@localhost bin]# ls -l java*
-rwxr-xr-x  1 root root  64492 Apr 13 06:55 java
-rwxr-xr-x  1 root root  71632 Apr 13 06:55 javac
-rwxr-xr-x  1 root root  71600 Apr 13 06:57 javadoc
-rwxr-xr-x  1 root root  71600 Apr 13 06:57 javah
-rwxr-xr-x  1 root root  71600 Apr 13 07:29 javap
-r-xr-xr-x  1 root root   1789 Apr 13 07:27 java-rmi.cgi
-rwxr-xr-x  1 root root 175978 Apr 13 07:54 javaws

// __ 2. you can compile java source files from the command prompt, without any
problems

// __ 3. you can make system/OS's calls from a java source file

import java.io.*;
import java.util.*;

class SysExec00{
private Runtime RT;
// __
SysExec00(){ RT = Runtime.getRuntime(); }
// __
public String[] exec(String[] aCmmnd){
 ArrayList<String> ALS = new ArrayList<String>();
 String[] aSAr = null;
// __
 try{
  Process Prx = RT.exec(aCmmnd);
  BufferedReader BR = new BufferedReader(new InputStreamReader(Prx.getInputStream()));
  String aLn = BR.readLine();
  while(aLn != null){ ALS.add(aLn); aLn = BR.readLine(); }
 }catch(IOException IOX){ IOX.printStackTrace(); }
// __
 int iSz = ALS.size();
 if(iSz > 0){ aSAr = new String[iSz]; ALS.toArray(aSAr); }
// __
 return(aSAr);
}
}

// __
public class javac02{
public static void main(String[] aArgs){

// __ OS calls are fine
 String[] aOut;
 String[] aCmmnd;
 SysExec00 SEx = new SysExec00();
// __
 aCmmnd = new String[]{"ps","-aux"};
 aOut = SEx.exec(aCmmnd);
 if((aOut != null) && (aOut.length > 0)){
  for(int k = 0; (k < aOut.length); ++k){
   System.out.println("// __ aOut[" + k + "]: |" + aOut[k] + "|");
  }
 }// ((aOut != null) && (aOut.length > 0))

// __
 aCmmnd = new String[]{"ls","-l"};
 aOut = SEx.exec(aCmmnd);
 if((aOut != null) && (aOut.length > 0)){
  for(int k = 0; (k < aOut.length); ++k){
   System.out.println("// __ aOut[" + k + "]: |" + aOut[k] + "|");
  }
 }// ((aOut != null) && (aOut.length > 0))

/*
// __ how to echo an environment variable?
 aCmmnd = new String[]{"echo","$PATH"};
 aOut = SEx.exec(aCmmnd);
 if((aOut != null) && (aOut.length > 0)){
  for(int k = 0; (k < aOut.length); ++k){
   System.out.println("// __ aOut[" + k + "]: |" + aOut[k] + "|");
  }
 }// ((aOut != null) && (aOut.length > 0))
*/

// __ but trying to compile a class fails
 aCmmnd = new String[]{"javac", "./test00.java"};
 aOut = SEx.exec(aCmmnd);
 if((aOut != null) && (aOut.length > 0)){
  for(int k = 0; (k < aOut.length); ++k){
   System.out.println("// __ aOut[" + k + "]: |" + aOut[k] + "|");
  }
 }// ((aOut != null) && (aOut.length > 0))
}
}

// __ 4. however trying to compile this simple piece of code:

import java.util.*;

public class test00{
test00(){}
// __
public String getTime(){ return(new Date()); }
// public String getTime(){ return(new Date().toString()); }
// __
public static void main(String[] aArgs){
 test00 t = new test00();
 System.err.println(t.getTime());
}
}

gives you:
[root@localhost XSD02]# javac test00.java
test00.java:6: incompatible types
found   : java.util.Date
required: java.lang.String
public String getTime(){ return(new Date()); }
                                ^
1 error

// __ 5. BUT NO ERRROS ARE SHOWN WHEN YOU DO THE COMPILING FROM WITHIN A RUNNING JAVA APP CALLING as tried through (see code snippet above):
...
 aCmmnd = new String[]{"javac", "./test00.java"};
 aOut = SEx.exec(aCmmnd);
...
NO ERRORS ARE REPORTED

// __ 6. fixing the code will allowed for the compilation of the class

How do you get the errors from the compilation tried within a running JVM?
lbrtchx@hotmail.com <Albretch Muller>