breakpoint error when debugging in eclipse, how to fix it

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Java

Eclipse

debugging

Need to debug a jar file "ProA",so import the sourcecode in the project, but there is a strange error in Eclipse while trying to set a breakpoint. detail as below:
[Unable to install breakpoint due to missing line number attributes,Modify compiler options togenerate line number attributes]

i have try to several method to solve, but failed.
1) Under "Window --> Preferences --> Java --> Compiler --> Classfile Generation", all options have to be to True
2) In .settings folder of your project, look for a file called org.eclipse.jdt.core.prefs. Verify or set org.eclipse.jdt.core.compiler.debug.lineNumber=generate
3) add the "debug=true" flag in the build.xml,just like this:

<javac debug="true" ...>

Any help will be appreciated.