java - Can I "convert" ParseTree to CommonTree in ANTLR? -

i want construct subtrees of parsetree, class contains insertchild(index,object) method seems commontree, , cannot pass rulecontext type object, because tries convert tree object, , "java.lang.classcastexception: java8parser$classdeclarationcontext cannot cast org.antlr.runtime.tree.tree" exception.

any ideas? thanks. (edit: added code)

private void getsubtrees(parsetree tree){     commontree commontree = new commontree();     setrecursivedescendants(commontree, tree); }  private commontree setrecursivedescendants(commontree commontree,parsetree parsetree){     int n = parsetree.getchildcount();         (int = 0; < n; i++) {             commontree.insertchild(i, parsetree.getchild(i);             setrecursivedescendants(commontree, parsetree.getchild(i));         }         return commontree; }