19.1.3 Problem #3: Field Declaration versus Method Declaration

Consider the two productions (shown after problem #2 has been corrected):

FieldDeclaration:

	Modifiersopt Type VariableDeclarators ;

and:

MethodHeader:

	Modifiersopt ResultType MethodDeclarator Throwsopt

where ResultType is defined as:

ResultType:

	Type

	void

Now consider the partial input:

class Problem3 { int julie

Note that, in this simple example, no Modifiers are present. When the parser is considering the token int, with one-token lookahead to symbol julie, it cannot yet tell whether this will be a field declaration such as:

int julie = 14;

or a method declaration such as:

int julie(String art) { return art.length(); }

Therefore, after the parser reduces int to the nonterminal Type, it cannot tell with only one-token lookahead whether Type should be further reduced to ResultType (for a method declaration) or left alone (for a field declaration). Therefore, the productions shown above result in a grammar that is not LALR(1).

The solution is to eliminate the ResultType production and to have separate alternatives for MethodHeader:

MethodHeader:

	Modifiersopt Type MethodDeclarator Throwsopt

	Modifiersopt void MethodDeclarator Throwsopt

This allows the parser to reduce int to Type and then leave it as is, delaying the decision as to whether a field declaration or method declaration is in progress.