LL(1)递归下降

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package com.parting_soul.LL1Analyze;import java.util.Scanner;/** * 递归下降 * Created by parting_soul on 17-4-12. * <p> * S->AaS * S->BbS * S->d * A->a * B->^ * B->c * <p> * select(S->AaS) = {a} * select(S->BbS) = {b,c} * select(S->d) = {d} * select(A->a) = {a} * select(B->^) = {b} * select(B->c) = {c} */public class LL1Analyze {    private String textContent;    private int currentPos;    private ErrorException exception;    public LL1Analyze() {        exception = new ErrorException("语法错误");    }    public static void main(String[] args) {        LL1Analyze analyze = new LL1Analyze();        Scanner in = new Scanner(System.in);        String str = null;        System.out.println("输入待匹配串:");        while ((str = in.nextLine()) != null) {            analyze.setTextContent(str);            try {                analyze.start();            } catch (ErrorException e) {                System.out.println(e.getMessage());            }            analyze.init();            str = null;            System.out.println("输入待匹配串:");        }    }    public void init() {        currentPos = 0;        textContent = null;    }    /**     * 从开始符开始匹配     */    private void start() throws ErrorException {        parseStart();        if (currentPos < textContent.length()) {            //若未匹配完全,则也为语法错误            throw exception;        }        System.out.println("语法分析正确");    }    private void error() throws ErrorException {        throw exception;    }    public void setTextContent(String textContent) {        this.textContent = textContent;    }    /**     * 匹配终结符     *     * @param pattern     */    public void matchTerminal(char pattern) throws ErrorException {        if (currentPos >= textContent.length()) throw exception;        char currentC = textContent.charAt(currentPos);        if (currentC != pattern) {            error();        } else {            currentPos++;        }    }    private void parseStart() throws ErrorException {        if (currentPos >= textContent.length()) throw exception;        char currentC = textContent.charAt(currentPos);        switch (currentC) {            case 'a':                //select(S->AaS)                parseA();                matchTerminal('a');                parseStart();                break;            case 'b':            case 'c':                //select(S->BbS);                parseB();                matchTerminal('b');                parseStart();                break;            case 'd':                //select(S->d)                matchTerminal('d');                break;            default:                error();                break;        }    }    public void parseA() throws ErrorException {        if (currentPos >= textContent.length()) throw exception;        char currentC = textContent.charAt(currentPos);        switch (currentC) {            case 'a':                //select(A->a)                matchTerminal('a');                break;            default:                error();                break;        }    }    public void parseB() throws ErrorException {        if (currentPos >= textContent.length()) throw exception;        char currentC = textContent.charAt(currentPos);        switch (currentC) {            case 'b':                //select(B->^)                break;            case 'c':                //select(B->c)                matchTerminal('b');                break;            default:                error();                break;        }    }}class ErrorException extends Exception {    public ErrorException(String msg) {        super(msg);    }}
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