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Manifest Specification

John Smith
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Joined: Oct 08, 2001
Posts: 2937
For a long time, I've thought that the only way to specify the main class attribute in a jar manifest is like this:
Main-Class: mypackage.MyMainClass
However, someone suggested that it can also be
Main-Class: mypackage/MyMainClass
And it turned out that both versions work. I looked at Sun's Jar File Specification, but couldn't find and references as to how exactly the main class attribute should be delimited. The only thing that it says is "Main-Class :
The value of this attribute defines the relative path of the main application class which the launcher will load at startup time. The value must not have the .class extension appended to the class name.
".
Does anyone know if there is a difference between the two different way of delimiting the "Main-Class" attribute?
Thanks,
Eugene.
Maulin Vasavada
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Joined: Nov 04, 2001
Posts: 1871
hi Eugene,
i guess both works fine as we use the jar file.
1. the package access via "."
this works as java class loader parses the fully qualified class name and "resolves" all "." and replaces them with "/".
then the class loader tries to find that directory path in the CLASSPATH and if it finds it then loades the class from directory : packagename. so essentially, if my package is,
"earth.myhome" then after "resolving" it will be,
earth/myhome and if the class is "myTV" then it will look for , earth/myhome/myTV.class in the Jar...

now, in Jar file (that follows the standard zip format if i'm not mistaken), we have the directory based storage , right? so, now when the class loader encounters the packaged class, it "resolves" the packagename for the class and then looks for that package directory in the Jar. it works if the directory is Jarred in there.

2. for the "/" operator in Main-Class,
here also it works due to the "resolve" mechanism as the "."s gets converted into "/" ...
so i guess both works...
regards
maulin
Maulin Vasavada
Ranch Hand

Joined: Nov 04, 2001
Posts: 1871
hi
sorry..i miswrote in 2nd option explanation..
it works in 2nd case ("/") as ultimately everything is resolved via "/" (as u notice in 1st option, "." are converted to "/")...
so its like,
1st option is a extension to the 2nd option where we are also allowed to put "." and follow the standard java package convention instead of using "/" ...
regards
maulin
 
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subject: Manifest Specification