You should have an explicit Symbol class, with methods toString and equals in addition to a constructor that takes a String as argument. The equals method should determine whether two symbols print the same.

Grammars are to be represented by instances of a Grammar class. This class is to have a constructor that takes as its single argument a Symbol that is to be the start symbol of the grammar. The class is to have a void method addNonterminal that takes a symbol and adds it to the collection of nonterminal symbols for the grammar. The class is to have three void methods addRule, taking respectively 2, 3, and 4 Symbols as arguments, that add rules to the grammar. In each case, the first symbol is to be interpreted as the left-hand side, and the other symbols as the symbols of the right-hand side, in order. Finally, the class is to have a method getYields that takes a Symbol and an int n, and returns a List of all strings of length n that can be generated from the given symbol.

You will probably find it convenient to have a separate Rule class to represent grammar rules.

Test your class definitions with the code in the file A1.java, which is available on the class web site.