When I'm looking at ASTNodes in Eclipse, how can I tell if one is in a valid state?

Question

When I'm going through the abstract syntax tree of a project in Eclipse how can I tell if a TypeDeclaration is in a valid state (ie, will compile)? I have tried calling type.getFlags() but it always returns 2 (ASTNode.ORIGINAL) even when it's a type I know is not valid (ie it implements an interface that doesn't exist).

Is there a way to do this?