ParserATNSimulator.java 文件源码

/**
 * Add an edge to the DFA, if possible. This method calls
 * {@link #addDFAState} to ensure the {@code to} state is present in the
 * DFA. If {@code from} is {@code null}, or if {@code t} is outside the
 * range of edges that can be represented in the DFA tables, this method
 * returns without adding the edge to the DFA.
 *
 * <p>If {@code to} is {@code null}, this method returns {@code null}.
 * Otherwise, this method returns the {@link DFAState} returned by calling
 * {@link #addDFAState} for the {@code to} state.</p>
 *
 * @param dfa The DFA
 * @param from The source state for the edge
 * @param t The input symbol
 * @param to The target state for the edge
 *
 * @return If {@code to} is {@code null}, this method returns {@code null};
 * otherwise this method returns the result of calling {@link #addDFAState}
 * on {@code to}
 */
protected DFAState addDFAEdge(@NotNull DFA dfa,
                              @Nullable DFAState from,
                              int t,
                              @Nullable DFAState to)
{
    if ( debug ) {
        System.out.println("EDGE "+from+" -> "+to+" upon "+getTokenName(t));
    }

    if (to == null) {
        return null;
    }

    to = addDFAState(dfa, to); // used existing if possible not incoming
    if (from == null || t < -1 || t > atn.maxTokenType) {
        return to;
    }

    synchronized (from) {
        if ( from.edges==null ) {
            from.edges = new DFAState[atn.maxTokenType+1+1];
        }

        from.edges[t+1] = to; // connect
    }

    if ( debug ) {
        System.out.println("DFA=\n"+dfa.toString(parser!=null?parser.getTokenNames():null));
    }

    return to;
}