Differences between java -cp and java -jar

Question

What is the difference between running a Java application withjava -cp CLASSPATH and java -jar JAR FILE PATH  Is one of them preferred to the other for running a Java application  I mean which one of these ways is more expensive for JVM  according to their machine resources usage    Which one will cause JVM to spawn more threads while trying to run the application

User · Accepted Answer

I prefer the first version to start a java application just because it has less pitfalls ("welcome to classpath hell"). The second one requires an executable jar file and the classpath for that application has to be defined inside the jar's manifest (all other classpath declaration will be silently ignored...). So with the second version you'd have to look into the jar, read the manifest and try to find out if the classpath entries are valid from where the jar is stored... That's avoidable.

I don't expect any performance advantages or disadvantages for either version. It's just telling the jvm which class to use for the main thread and where it can find the libraries.

User · Answer

Like already said  the -cp is just for telling the jvm in the command line which class to use for the main thread and where it can find the libraries  define classpath   In -jar it expects the class-path and main-class to be defined in the jar file manifest  So other is for defining things in command line while other finding them inside the jar manifest  There is no difference in performance  You can t use them at the same time  -jar will override the -cp   Though even if you use -cp  it will still check the manifest file  So you can define some of the class-paths in the manifest and some in the command line  This is particularly useful when you have a dependency on some 3rd party jar  which you might not provide with your build or don t want to provide  expecting it to be found already in the system where it s to be installed for example   So you can use it to provide external jars  It s location may vary between systems or it may even have a different version on different system  but having the same interfaces   This way you can build the app with other version and add the actual 3rd party dependency to class-path on the command line when running it on different systems

User · Answer

java -cp CLASSPATH is necesssary if you wish to specify all code in the classpath  This is useful for debugging code   The jarred executable format  java -jar JarFile can be used if you wish to start the app with a single short command  You can specify additional dependent jar files in your MANIFEST using space separated jars in a Class-Path entry  e g    Class-Path  mysql jar infobus jar acme beans jar   Both are comparable in terms of performance

User · Answer

With the -cp argument you provide the classpath i e  path s  to additional classes or libraries that your program may require when being compiled or run  With -jar you specify the executable JAR file that you want to run   You can t specify them both  If you try to run java -cp folder myexternallibrary jar -jar myprogram jar then it won t really work  The classpath for that JAR should be specified in its Manifest  not as a -cp argument   You can find more about this here and here   PS  -cp and -classpath are synonyms

User · Answer

When using java -cp you are required to provide fully qualified main class name  e g   java -cp com mycompany MyMain  When using java -jar myjar jar your jar file must provide the information about main class via manifest mf contained into the jar file in folder META-INF   Main-Class  com mycompany MyMain

User · Answer

There won t be any difference in terms of performance  Using java - cp we can specify the required classes and jar s in the classpath for running a java class file   If it is a executable jar file   When java -jar command is used  jvm finds the class that it needs to run from  META-INF MANIFEST MF file inside the jar file

[java] Differences between "java -cp" and "java -jar"?

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