[antlr-interest] Inheritance of BaseAST class

[FC]

I am now working on transforming the AST parsed on
java code to xml file. I use the example of java
parser in Antlr-2.7.3 package as follows.

//JavaRecognizer is a subclass of class 
//antlr.LLkParser 
JavaLexer lexer = new JavaLexer(r);
lexer.setFilename(f);
JavaRecognizer parser = new JavaRecognizer(lexer);
parser.setFilename(f);
parser.compilationUnit();

//JavaAST is extended from BaseAST, and the XML 
//serialization methods in BaseAST are overriden	
JavaAST t = (JavaAST)parser.getAST();
Writer w = new OutputStreamWriter(System.out);
t.xmlSerialize(w);
w.write("\n");
w.flush();

But there is run-time error: 
parser exception: java.lang.ClassCastException at line
of "JavaAST t = (JavaAST)parser.getAST();", that is,
the AST object can not be casted to my subclass
JavaAST. How can I solve this problem? 

thanks

Ted


		
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