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class file has wrong version 51.0，should be 49.0 [message #1703552]

Mon, 03 August 2015 04:16

frank ho

Messages: 5
Registered: June 2015

Junior Member

Dear All,

I have 2 jdk in my computer, one is 1.7 and another is 1.5. I got a eclipse from my co-worker, checkout project from svn, complied it successful. However, there is error : class file has wrong version 51.0，should be 49.0 when I run it in eclipse( this is google gwt project).

One of my colleague said I should modify one cache file under the eclipse direcotry, but he forgot the loaction of this file.

Anyone knows?

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Re: class file has wrong version 51.0，should be 49.0 [message #1703591 is a reply to message #1703552]

Mon, 03 August 2015 12:56

Erick Hagstrom

Messages: 107
Registered: April 2014
Location: USA

Senior Member

Your class file was compiled under Java 1.7. You're running it with Java 1.5. That doesn't work. You either need to recompile it with Java 1.5 or run it with Java 1.7. See https://en.wikipedia.org/wiki/Java_class_file#General_layout (refer to byte offset 6 & 7 in the table) for more information.

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Re: class file has wrong version 51.0，should be 49.0 [message #1703824 is a reply to message #1703591]

Wed, 05 August 2015 08:46

frank ho

Messages: 5
Registered: June 2015

Junior Member

After modified this file : org.eclipse.jdt.launching.prefs under : <project folder>\.metadata\.plugins\org.eclipse.core.runtime\.settings, this problem has been fixed. The modification is : add

<libraryLocations>\r\n<libraryLocation 
jreJar\="D\:/Java/jdk7/jre/lib/resources.jar" 
jreJavadoc\="http\://docs.oracle.com/javase/7/docs/api/" 
jreSrc\="D\:/Java/jdk7/src.zip" pkgRoot\=""/>\r\n

to it.

But my questions are :

1. what is this file used for?
2. when use this file?
3. why I have to add these information to it by hand rather than generate these automatically when I set jdk in eclipse preference?
4. why this error occur if this file doesn't has <libraryLocations> when running project(the project compile success before running)?

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Re: class file has wrong version 51.0，should be 49.0 [message #1703826 is a reply to message #1703591]

Wed, 05 August 2015 08:47

frank ho

Messages: 5
Registered: June 2015

Junior Member

After modified this file : org.eclipse.jdt.launching.prefs under : <project folder>\.metadata\.plugins\org.eclipse.core.runtime\.settings,

this problem has been fixed.

The modification is :
add

<libraryLocations>\r\n<libraryLocation 
jreJar\="D\:/Java/jdk7/jre/lib/resources.jar" 
jreJavadoc\="http\://docs.oracle.com/javase/7/docs/api/" 
jreSrc\="D\:/Java/jdk7/src.zip" pkgRoot\=""/>\r\n.........

to it.

eclipse is :

Eclipse Java EE IDE for Web Developers.

Version: Luna Release (4.4.0)
Build id: 20140612-0600

my questions are :

1. what is this file used for?
2. when use this file?
3. why I have to add these information to it by hand rather than generate these automatically when I set jdk in eclipse preference?
4. why this error occur if this file doesn't has <libraryLocations> when running project(the project compile success before running)?

[Updated on: Fri, 07 August 2015 03:00]

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