File	Doc	Category	Size	Date	Package
non_terminal.java	API Doc	Java SE 5 API	9471	Fri Aug 26 14:54:54 BST 2005	com.sun.java_cup.internal

non_terminal

• java.lang.Object
  • symbol

Fields Summary
protected static Hashtable	_all Table of all non-terminals -- elements are stored using name strings as the key
protected static Hashtable	_all_by_index Table of all non terminals indexed by their index number.
protected static int	next_index Static counter to assign unique indexes.
protected static int	next_nt Static counter for creating unique non-terminal names
public static final non_terminal	START_nt special non-terminal for start symbol
public boolean	is_embedded_action flag non-terminals created to embed action productions
protected Hashtable	_productions Table of all productions with this non terminal on the LHS.
protected boolean	_nullable Nullability of this non terminal.
protected terminal_set	_first_set First set for this non-terminal.

Constructors Summary
public non_terminal(String nm, String tp) Full constructor. param nm the name of the non terminal. param tp the type string for the non terminal. /* super class does most of the work */ super(nm, tp); /* add to set of all non terminals and check for duplicates */ Object conflict = _all.put(nm,this); if (conflict != null) // can't throw an exception here because these are used in static // initializers, so we crash instead // was: // throw new internal_error("Duplicate non-terminal ("+nm+") created"); (new internal_error("Duplicate non-terminal ("+nm+") created")).crash(); /* assign a unique index */ _index = next_index++; /* add to by_index set */ _all_by_index.put(new Integer(_index), this);
public non_terminal(String nm) Constructor with default type. param nm the name of the non terminal. this(nm, null);

Methods Summary
public void	add_production(production prod) Add a production to our set of productions. /* catch improper productions */ if (prod == null || prod.lhs() == null || prod.lhs().the_symbol() != this) throw new internal_error( "Attempt to add invalid production to non terminal production table"); /* add it to the table, keyed with itself */ _productions.put(prod,prod);
public static java.util.Enumeration	all() Access to all non-terminals. return _all.elements();
public static void	compute_first_sets() Compute first sets for all non-terminals. This assumes nullability has already computed. boolean change = true; Enumeration n; Enumeration p; non_terminal nt; production prod; terminal_set prod_first; /* repeat this process until we have no change */ while (change) { /* look for a new change */ change = false; /* consider each non-terminal */ for (n = all(); n.hasMoreElements(); ) { nt = (non_terminal)n.nextElement(); /* consider every production of that non terminal */ for (p = nt.productions(); p.hasMoreElements(); ) { prod = (production)p.nextElement(); /* get the updated first of that production */ prod_first = prod.check_first_set(); /* if this going to add anything, add it */ if (!prod_first.is_subset_of(nt._first_set)) { change = true; nt._first_set.add(prod_first); } } } }
public static void	compute_nullability() Compute nullability of all non-terminals. boolean change = true; non_terminal nt; Enumeration e; production prod; /* repeat this process until there is no change */ while (change) { /* look for a new change */ change = false; /* consider each non-terminal */ for (e=all(); e.hasMoreElements(); ) { nt = (non_terminal)e.nextElement(); /* only look at things that aren't already marked nullable */ if (!nt.nullable()) { if (nt.looks_nullable()) { nt._nullable = true; change = true; } } } } /* do one last pass over the productions to finalize all of them */ for (e=production.all(); e.hasMoreElements(); ) { prod = (production)e.nextElement(); prod.set_nullable(prod.check_nullable()); }
static com.sun.java_cup.internal.non_terminal	create_new(java.lang.String prefix) Method for creating a new uniquely named hidden non-terminal using the given string as a base for the name (or "NT$" if null is passed). param prefix base name to construct unique name from. /* added 24-Mar-1998, CSA */ /*-----------------------------------------------------------*/ /*--- Static Methods ----------------------------------------*/ /*-----------------------------------------------------------*/ if (prefix == null) prefix = "NT$"; return new non_terminal(prefix + next_nt++);
static com.sun.java_cup.internal.non_terminal	create_new() static routine for creating a new uniquely named hidden non-terminal return create_new(null);
public static com.sun.java_cup.internal.non_terminal	find(java.lang.String with_name) lookup a non terminal by name string if (with_name == null) return null; else return (non_terminal)_all.get(with_name);
public static com.sun.java_cup.internal.non_terminal	find(int indx) Lookup a non terminal by index. Integer the_indx = new Integer(indx); return (non_terminal)_all_by_index.get(the_indx);
public terminal_set	first_set() First set for this non-terminal. return _first_set;
public boolean	is_non_term() Indicate that this symbol is a non-terminal. return true;
protected boolean	looks_nullable() Test to see if this non terminal currently looks nullable. /* look and see if any of the productions now look nullable */ for (Enumeration e = productions(); e.hasMoreElements(); ) /* if the production can go to empty, we are nullable */ if (((production)e.nextElement()).check_nullable()) return true; /* none of the productions can go to empty, so we are not nullable */ return false;
public boolean	nullable() Nullability of this non terminal. return _nullable;
public int	num_productions() Total number of productions with this non terminal on the LHS. return _productions.size();
public static int	number() Total number of non-terminals. return _all.size();
public java.util.Enumeration	productions() Access to productions with this non terminal on the LHS. return _productions.elements();
public java.lang.String	toString() convert to string return super.toString() + "[" + index() + "]" + (nullable() ? "*" : "");