How to set the -Xmx when start running a jar file?

Unfortunately, existing answers are wrong in one crucial point.

-Xmx must be passed to the Java runtime environment, not to the executed jar.

Wrong:

java -jar JavaApplication.jar -Xmx1024m 

Correct:

java -Xmx1024m -jar JavaApplication.jar 

More specifically, the java launcher needs to be used as follows:

java [options] -jar file.jar [arguments]

• [options] are passed to the Java runtime environment
• [arguments] are passed to the main function

The -Xmx parameter belongs to the (nonstandard) JVM options, and--being an option--needs to be listed before -jar (or at least before file.jar). The JVM will not recognize an -Xmx argument passed to the main function as proposed in other answers.

try java -Xmx1024m filename.

I found this on StackOverflow What does Java option -Xmx stand for? and use it when I start Netbeans for instance.

use it like this

java -Xmx1024m -jar JavaApplication.jar

info: -Xmxn Specify the maximum size, in bytes, of the memory allocation pool. This value must be a multiple of 1024 greater than 2MB. Append the letter k or K to indicate kilobytes, or m or M to indicate megabytes. The default value is 64MB. The upper limit for this value will be approximately 4000m on Solaris 7 and Solaris 8 SPARC platforms and 2000m on Solaris 2.6 and x86 platforms, minus overhead amounts.

Three methods:

• Command Line:
• Instruct your users to run your application using "java -Xmx1024m -jar SampleJavaApp.jar"
• Java Control Panel:
• Instruct your users to dedicate more memory to java by default: Win7 guide
• Restart your jar with the appropriate Xmx value.

The last option is "evil" but doesn't require any extra effort from your users. Here's a sample block of code:

public static void main(String[] args) throws IOException, URISyntaxException {
    String currentPath=SampleJavaApp.class
          .getProtectionDomain()
          .getCodeSource().getLocation()
          .toURI().getPath()
          .replace('/', File.separator.charAt(0)).substring(1);
    if(args.length==0 && Runtime.getRuntime().maxMemory()/1024/1024<980) {
        Runtime.getRuntime().exec("java -Xmx1024m -jar "+currentPath+" restart");
        return;
    }
}