flt.java

JAVA在编译原理上的应用。

package lolo.scans;

/** A class to scan for floating point numbers. Legal floating point numbers are:
 * <ul type=disc>
 * <li><tt>22</tt>, <tt>22.</tt>, <tt>22.2</tt>, <tt>.22</tt>
 * <li><tt>22e2</tt>, <tt>22.e2</tt>, <tt>22.2e2</tt>, <tt>.22e2</tt>
 * <li><tt>22e+2</tt>, <tt>22.e+2</tt>, <tt>22.2e+2</tt>, <tt>.22e+2</tt>
 * <li><tt>22e-2</tt>, <tt>22.e-2</tt>, <tt>22.2e-2</tt>, <tt>.22e-2</tt>
 * </ul>
 *
 * A leading sign (<tt>+</tt> or <tt>-</tt>) can be switched on or off.
 *
 * @author <a href="http://www.inf.uos.de/bernd" target="_blank">Bernd K&uuml;hl</a>
           (<a href="mailto:[e-mail]">[e-mail]</a>)
 */
public class Flt extends Scan {
    /** The legal characters. */
    protected static final String chars = "+-.0123456789eE";
    /** The state table. */
    protected static final int newState [][] = {
        // current state, input => newstate
        //+  -  .  0  1  2  3  4  5  6  7  8  9  e  E
        { 8, 8, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 8, 8 },  // state 0
        { 8, 8, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 8, 8 },  // state 1
        { 8, 8, 4, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 5, 5 },  // state 2
        { 8, 8, 8, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 8, 8 },  // state 3
        { 8, 8, 8, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5 },  // state 4
        { 6, 6, 8, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8 },  // state 5
        { 8, 8, 8, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8 },  // state 6
        { 8, 8, 8, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8 },  // state 7
        { 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8 }   // state error
    };
    /** The current state. */
    protected transient int state;
    
    /** Does this recognizer scan a leading sign. */
    protected boolean allowLeadingSign;
    
    /** Returns wether a leading sign is scanned.
     *
     * @return returns wether a leading sign is scanned.
     */
    public boolean getAllowLeadingSign() { return allowLeadingSign; }

    /** Constructs a Flt and sets wether a leading sign is scanned.
     *
     * @params bol marks if a leading sign is scanned.
     */
    public Flt(boolean bol) {
        newState[0] = (allowLeadingSign = bol) ?
            new int[] { 1, 1, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 8, 8 } :
            new int[] { 8, 8, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 8, 8 };
    }

    /** Constructs a Flt and sets no leading sign. */
    public Flt() {
        this(false);
    }
    
    public void reset() {
        state = 0;
//System.err.println("\treset "+this);
    }
    
    public State nextChar(char ch) {
        // is ch a legal input character?
        int input;
        if ((input = chars.indexOf((int) ch)) < 0)
            return stateObject.set(
                false,  // more
                false   // found
            );
    
        boolean found = false, more = false;
//System.err.print("\told state "+state+", input "+input+", ch "+ch+", new state ");
        state = newState[state][input];
//System.err.println(state);
        switch(state) {
            case 8:	 break;    // error state, parse ends
            case 0:	 new RuntimeException("illegal state "+state); // cann't be..
            case 1:	 more = true; break;
            case 2:	 found = more = true; break;
            case 3:	 more = true; break;
            case 4:	 found = more = true; break;
            case 5:	 more = true; break;
            case 6:	 more = true; break;
            case 7:	 found = more = true; break;
            default: new RuntimeException("illegal state "+state); // cann't be..
        }
                    
        return stateObject.set(more, found);
    }

    /** Indicates whether some other object is &quot;equal to&quot; this one.
     *
     * @return Indicates whether some other object is &quot;equal to&quot; this one.
     */
    public boolean equals(Object obj) {
        if (obj == null || !(obj instanceof Flt)) return false;
        return this.allowLeadingSign == ((Flt) obj).allowLeadingSign;
    }
    
}