Eclipse ICompilationUnit

Compared to concrete class CompilationUnit, ICompilation is an interface as the "I" prepended.
It's for Type representation where as CompilationUnit is for AST representation, and parser object links between the two using Parser#setSource(ICompilationUnit); and parser.createAST(null).

In order to get the ICompilationUnit from java source code, you need to start from Workspace, IProject, IJavaProject and then find IType(The by using findType(TYPE_NAME).

References

• How you can get CompilationUnit (AST) from Workspace in eclipse?