What Does Java Option -Xmx Stand For

What does the java option -XX:-EliminateAllocations do?

This key disables "Scalar replacement optimization"

Simply spoken when an object is identified as non-escaping the JVM can replace its allocation on the heap with an allocation of its members on the stack which mitigates the lack of user guided stack allocation. The optimization is enabled by default since JDK 6U23 in the hotspot server compiler.

More info.

is It same mean JAVA_ARGS and JAVA OPTS

The only thing that is important is what the actual arguments are in the "-XX:MaxPermSize=512m -Xms512m -Xmx1024m".

What you call the environment variables is up to you for the most part, it is whatever the scripts you want to use it are expecting.

Java Options usage

Initially, i thought that + would mean enabling while - would mean disabling.

This is correct, according to the official documentation: "Boolean options are turned on with -XX:+<option> and turned off with -XX:-<option>."

But, if we want any option disabled than why even pass it along the command line?

That's because some may be enabled and others disabled per default, and this may change between Java releases.

Basic beginners in Java: what does 'arguments' mean in Java

Arguments is a list of Parameters that can be passed to your Java Programm at start up.

if (arguments.length > 0) checks if any arguments have been provided.

As otherwise you will be trying to access an empty array and get and index out of bounds exception.

Also there are pleanty of tutorials out there, that can help you.

Have a look at Oracle's essentials guide, here about CMD Line Arguments.

Proper usage of Java -D command-line parameters

I suspect the problem is that you've put the "-D" after the -jar. Try this:

java -Dtest="true" -jar myApplication.jar

From the command line help:

java [-options] -jar jarfile [args...]

In other words, the way you've got it at the moment will treat -Dtest="true" as one of the arguments to pass to main instead of as a JVM argument.

(You should probably also drop the quotes, but it may well work anyway - it probably depends on your shell.)

In Java -D what does the D stand for?

I've always assumed it was to define the value of a property... possibly a legacy from C compilers, which often use -D as similar to #define in code.

EDIT: The closest I have to a source for this at the moment is some JDK 1.1 documentation which specifies the flag as:

Redefines a property value. propertyName is the name of the property whose value you want to change and newValue is the value to change it to. [...]

That at least contains the word "redefine" which is close to "define" :)

How to get VM arguments from inside of Java application?

With this code you can get the JVM arguments:

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
...
RuntimeMXBean runtimeMxBean = ManagementFactory.getRuntimeMXBean();
List<String> arguments = runtimeMxBean.getInputArguments();