getBoolean in Java.lang

[munnanext]

public class getBooleanDemo {

public static void main(String args[]){
boolean b;
String propertyName ="true";
b = Boolean.getBoolean(propertyName);
System.out.println(b);
}

}

Can you pl explain me what getBoolean does ?
I am reading this in the Book and it says propertyName should be system property. I am not clear.

Thanks for solution

 

[stefanwagner]

A system-property is something special.
Your propertyName has nothing to do with it - it's just a variable-name you use.

java.lang.System.getProperty (String key);

returns a value for a key.
Imagine System-Properties as key-value-pairs:

HOME=/home/munnanext
EDITOR=mcedit
LINES=25
COLUMNS=80
HUSHLOGIN=FALSE

now you may ask:

String hl = System.getProperty ("HUSHLOGIN");
boolean b = Boolean.getBoolean (bhl);

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[munnanext]

I really Appreciate your Reply. Thanks for the clarification.

 

[munnanext]

based on your reply I have written a program like below to read the windir (which is a system variable) in my system. but when I run the program it is return me null instead of C:\WINNT.

Any help ? Thanks

public class getSystemProperty {

public static void main(String args[]){
String h1;
//String propertyName ="true";
h1 = System.getProperty("windir");

System.out.println(h1);
}

}

 

[sedj]

You cannot do it like that.

System.getProprerty() only works for variables passed into the JVM using the "-D" switch.
EG :

java -Dwindir=something MyProg

You can however do it like this :

import java.io.*;
public class Test {
 	public static void main(String args[]) throws Exception {

		Process p = Runtime.getRuntime().exec("cmd /c set WINDIR");
		p.waitFor();
		BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
		String envVar = br.readLine();
		br.close();

		System.out.println(envVar);
	}
}

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[munnanext]

I am intrested more on the first option. Sorry I couldn't able to follow you completely.

I am running the program like this
---------------------------------------
java -Dwindir=something readSystemVariable

I got hte following output
---------------------------------------
This is from the application something

My Source is
---------------------------------------

public class readSystemVariable{

public static void main(String args[]){
try{
String h1 = new String(System.getProperty ("windir"));
System.out.println("This is from the application "+ h1);
}catch( Exception e)
{
e.toString();
}
}

}

my Expected output is
------------------------
C:\winnt (Which is in my System variable value)

Apprecite your help

 

[sedj]

try :

java -Dwindir=%WINDIR% MyProg

If that doesn't work, then you will have to use the method I suggested before.

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[munnanext]

This is working thanks.

 

[stefanwagner]

For some properties you may use:

			System.out.println ("-----------------------Properties: ---------------");
		Properties p = System.getProperties ();
		p.list (System.out);
		System.out.println ("-----------------------and here env:--------------");
		Map <String, String> m = System.getenv ();
		Set<Map.Entry<String, String>> s = m.entrySet ();
		for (Map.Entry me : s)
		{
			System.out.println (me.getKey () + " = " + me.getValue ());
		}

Properties will probably not contain windir, but I bet you find your %WINDIR% with getenv().
Here a few values I found:

-----------------------Properties: ---------
-- listing properties --
java.vm.version=1.5.0-beta3-b57
path.separator=:
user.country=DE
user.dir=/home/stefan/proj/mini/forum
java.runtime.version=1.5.0-beta3-b57
os.arch=i386
java.io.tmpdir=/tmp
os.name=Linux
sun.jnu.encoding=ISO-8859-1
os.version=2.6.8.1
file.separator=/
sun.cpu.endian=little
-----------------------and here env:--------------
ANT_HOME = /usr/local/lib/ant
LANG = de_DE
PGDATA = /home/postgres/data
HZ = 100
_XKB_CHARSET = de-latin1-nodeadkeys
USER = stefan
SHELL = /bin/bash
QTDIR = /usr/lib/qt

remark: The code is 1.5.0-beta and might not work with 1.4.2.

Visit the docs for java.lang.System and find out, how to do it with java 1.4.x.


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[sedj]

Bear in mind that JVM System properties are completely different to environment properties - and the only way to get OS environment properties are as I demonstrated before.



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[stefanwagner]

sedj, while you're mostly right, the javadocs say:
java.lang.System.getenv:

getenv

public static Map<String,String> getenv()

Returns an unmodifiable string map view of the current system environment. The environment is a system-dependent mapping from names to values which is passed from parent to child processes.

And running a diff on the modified code above:

for (Map.Entry me : s)
{
    System.out.println (me.getKey () +"="+ me.getValue ());
}

and a plain 'env' on the commandline (plus sort in both cases and removing the Properties-part) shows 35 identical lines, 2 different and 2 additional for the java-getenv().

One of the differences is the invoking command - to no surprise, being /usr/bin/env in the one case and /opt/java/bin/java in the second.
The second is the LD_LIBRARY_PATH which is longer for the java-version, some java-dirs added.

The two additional java-entries are:

< NLSPATH=/usr/dt/lib/nls/msg/%L/%N.cat
< XFILESEARCHPATH=/usr/dt/app-defaults/%L/Dt

Unfortunately /usr/dt doesn't exist, so I have a broken java-installation?
And %L %N - do they mean language, nation? de DE in my case?

What's wrong with 'getenv ()'?
Ah - I see: new since 1.5

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