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This article will explain in detail how common JAVA virtual machine command line parameters are used. The content of the article is of high quality. Therefore, Xiaobian shares it with you as a reference. I hope that after reading this article, you will have a certain understanding of relevant knowledge.

Java virtual machine several command line parameters

I. Run class files

Execute a class file with main method, command behavior:

java

Note: CLASS file names do not have file suffix.class

For example:

javaTest

If the class file executed is packaged, that is, the class file uses:

package

That should be executed under the base path of the package, command behavior:

java.CLASS filename

For example:

PackageTest.java, its package name is com.ee2ee.test, the corresponding statement is:

packagecom.ee2ee.test;

PackageTest.java and the compiled class file PackageTest.class are stored in the following directory:

classes

|__com

|__ee2ee

|__test

|__PackageTest.java

|__PackageTest.class

To run PackageTest.class, execute under the classes directory:

javacom.ee2ee.test.PackageTest

Let's take a look at the usage of the second command-line parameter of the Java Virtual Machine.

Second, run the jar file class

The principle is the same as running a class file, just add the parameter-cp.

For example, execute the class com.ee2ee.test.PackageTest in test.jar with the following command line:

java-cptest.jarcom.ee2ee.test.PackageTest

Third, display jdk version information

When there are multiple versions of jdk on a machine, you need to know which version of jdk is currently in use. Use the parameter-version to know its version. Command behavior:

java-version

IV. Increase the *** memory that virtual machines can use

The amount of *** memory available to Java virtual machines is limited, and the default is usually 64MB or 128MB.

If an application loads data into memory in order to improve performance and occupies a large amount of memory, such as exceeding the default *** value of 128MB, you need to increase the *** memory available to the Java virtual machine, otherwise an Out of Memory exception will occur. When starting Java, you need to use the following two parameters:

- Memory size used when Xmsjava VM is initialized

- *** memory available for Xmxjava virtual machine

The size set in the above two parameters can have units, for example: 256m means 256MB

Examples:

java-Xms128m-Xmx256m...

Indicates that the Java virtual machine uses 128MB of memory for initialization and 256MB of available *** memory.

For tomcat, you can modify its script catalina.sh (unix platform) or catalina.bat (windows platform), and set the variable JAVA_OPTS, for example:

JAVA_OPTS='-Xms128m-Xmx256m' about common JAVA virtual machine command line parameter usage is how to share here, I hope the above content can have some help for everyone, you can learn more knowledge. If you think the article is good, you can share it so that more people can see it.

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