abstractlexicalanalysis.java

来自「<算法导论>第二版大部分算法实现. 1. 各类排序和顺序统计学相关」· Java 代码 · 共 90 行

/*
 * Copyright (C) 2003-2008 Wang Pengcheng <[e-mail]>
 * Permission is granted to copy, distribute and/or modify this
 * document under the terms of the GNU Free Documentation License,
 * Version 2.0 or any later version published by the Free Software Foundation;
 * with no Invariant Sections.
 * You may obtain a copy of the License at
 *   http://www.gnu.org/licenses/lgpl.txt
 */
//26 Feb 2008
package cn.edu.whu.iss.algorithm.unit10.expression.lexical;

/**
 * The abstract lexical analysis class.
 * 
 * @author wpc
 * @version 0.0.1
 */
public abstract class AbstractLexicalAnalysis implements LexicalAnalysis {

	/**
	 * The expression
	 */
	protected String expression;

	/**
	 * the constructor
	 */
	public AbstractLexicalAnalysis() {
		expression = "0";
	}

	/**
	 * The constructor
	 * 
	 * @param expr
	 *            the expression will be analysed
	 */
	public AbstractLexicalAnalysis(String expr) {
		this.expression = expr;
	}

	/**
	 * Check the char c is the permited char or not.
	 * @param c
	 * @return true that can be used
	 */
	protected boolean isPermitChar(char c) {
		for (int i = 0; i < PERMIT_CHAR.length; i++) {
			if (c == PERMIT_CHAR[i]) {
				return true;
			}
		}
		return false;
	}

	public String translateBracket(String expr) {
		if (expr != null) {
			this.expression = expr;
			return translateBracket();
		}
		return expr;
	}

	/**
	 * Translate the supported bracket to the aim.
	 * The expression is the object's expression.
	 * @return the 
	 */
	protected String translateBracket() {
		if (this.expression != null) {
			for (int i = 0; i < SUPPORT_BRACKET.length; i++) {
				expression = expression.replaceAll(SUPPORT_BRACKET[i], AIM_BRACKET[i]);
			}
		}
		return this.expression;
	}

	public String analyseExpr(String expr) {
		if(expr==null){
			return this.expression;
		}else {
			this.expression = expr;
			return analyseExpr();
		}
	}
	
	abstract protected String analyseExpr();
}