org.bidib.wizard.common.highlight.TextScanner Maven / Gradle / Ivy

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package org.bidib.wizard.common.highlight;

/**
 * This does exactly the same job as the Scanner class, but uses a table driven scanner. This illustrates how to extend
 * the Scanner class, and how a generator might produce a table-driven scanner (though this one was written by hand).
 * Public domain, no restrictions, Ian Holyer, University of Bristol.
 */
public class TextScanner extends Scanner {
    // Classify the 128 ASCII characters. Define a compact 'readable' form,
    // then expand into an array, using static initializer code. The 128 are:
    // .........tn..................... !"#$%&'()*+,-./0123456789:;<=>?
    // @ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~.

    static final String CS = "1111111112211111111111111111111127777774777774675555555555777777"
        + "7333333333333333333333333337777473333333333333333333333333377771";

    static final byte[] KINDS = new byte[CS.length()];
    static {
        for (int i = 0; i < CS.length(); i++) {
            KINDS[i] = (byte) (CS.charAt(i) - '0');
        }
    }

    // This state table has a row per scanner state, and a column per class of
    // character. Each entry is '-s' to mean accept the current character and
    // goto state s, or '+t' to mean end the token giving it type t. There is
    // no stack of states, or extra table to determine the next state after a
    // token is recognized, as there could be with more sophisticated scanners.
    // The raw numbers +t must use or match the constants in TokenTypes.

    static final int[][] TABLE = {
        // $ \0 \n z '-_ 9 . ( // $ = end of text, must be column 0
        { +1, -1, -2, -3, -4, -5, -4, -4 }, // s=0: start token
        { +1, +1, +1, +1, +1, +1, +1, +1 }, // s=1: illegal character (t=1)
        { +0, +0, -2, +0, +0, +0, +0, +0 }, // s=2: whitespace (t=0)
        { +2, +2, +2, -3, -3, -3, +2, +2 }, // s=3: word (t=2)
        { +4, +4, +4, +4, +4, +4, +4, +4 }, // s=4: punctuation (t=4)
        { +3, +3, +3, +3, +3, -5, -5, +3 } // s=5: number (t=3)
        };

    // Now all we have to do is to override read(), using the parent variables
    // buffer, start, end, state.

    /**
     * {@inheritDoc}
     */
    @Override
    protected int read() {
        state = 0;
        int kind = KINDS[buffer[start]];
        int type;
        while (true) {
            type = TABLE[state][kind];
            if (type >= 0) {
                break;
            }
            state = -type;
            start++;
            if (start >= end) {
                kind = 0;
            }
            else {
                kind = KINDS[buffer[start]];
            }
        }
        state = WHITESPACE;
        return type;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void initSymbolTable() { // NOSONAR
    }
}