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ANTLR will aggressively optimize out the rules that are not needed. It must still include rules whose lookahead DFA change as a result of an overridden rule. In this case, the change in rule type alters the lookahead prediction for rule decl. Consequently, decl must be included in the generated code for grammar Java. Here is the output ANTLR would generate for Java:
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class JavaParser extends Parser {
JavaDecl delegate = new JavaDecl(...); // probably set in ctor actually
public void type() { ... }
public void prog() { decl(); } // uses overridden version.
public void decl() {
int alt = predict-alt-of-decl; // DFA changed; must copy whole rule here
switch (alt) {
case 1 :
type(); match(ID); match(';');
case 2 :
type(); match(ID); init(); match(';');
}
}
void init() { delegate.init(); }
}
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