expressionreader.java

symbman（大学作业）

import java.io.*;
import java.util.Vector;
import java.util.Iterator;

public class ExpressionReader {
	private BufferedReader br;
	private FileReader fr;
	
	public ExpressionReader(String fileName) throws IOException {
			fr = new FileReader(fileName);
			br = new BufferedReader(fr);
	}
	
	private Expression parse(String s) throws InvalidExpressionException {
		if(s.matches("\\(\\(\\w+\\)=\\(.+\\)\\)")) {
			// Assign
			String sym = s.replaceAll("\\(\\((\\w+)\\)=\\(.+\\)\\)", "$1");
			String e = s.replaceAll("\\((\\(\\w+\\))=(\\(.+\\))\\)", "$2");
			
			return new Assign(new Symbol(sym), parse(e));
		}
		
		if(s.matches("\\(D\\(\\(.+\\),\\(.+\\)\\)")) {
			// Derive
			String e = s.replaceAll("\\(D\\((\\(.+\\)),(\\(.+\\))\\)", "$1");
			String sym = s.replaceAll("\\(D\\((\\(.+\\)),(\\(.+\\))\\)", "$2");
			
			return new Derive(parse(e), new Symbol(sym));
		}
		
		if(s.matches("\\((\\d*\\.\\d*|\\d+)\\)")) {
			// NumericValue
			String n = s.replaceAll("\\((\\d*\\.\\d*|\\d+)\\)","$1");
			return new NumericValue(new Double(n).doubleValue());
		}
		
		if(s.matches("\\((\\(.+\\))(\\+(\\(.+\\)))+\\)")) {
			// Plus
			Vector v = new Vector();
			while(s.matches("\\((\\(.+\\))(\\+(\\(.+\\)))+\\)")) {
				String last = s.replaceAll("\\((\\(.+\\))(\\+(\\(.+\\)))+\\)","$3");
				v.add(parse(last));
				s = "("+s.replaceAll("\\((\\(.+\\))(\\+(\\(.+\\)))+\\)","$1")+")";
			}
			
			v.add(parse(s.substring(1,s.length()-1)));
			
			Expression[] addends = new Expression[v.size()];
			for(int i=v.size()-1;i>=0;i--)
				addends[i]=(Expression)v.get(i);
			
			return new Plus(addends);
		}
		
		if(s.matches("\\((\\(.+\\))(\\*(\\(.+\\)))+\\)")) {
			// Times
			Vector v = new Vector();
			while(s.matches("\\((\\(.+\\))(\\*(\\(.+\\)))+\\)")) {
				String last = s.replaceAll("\\((\\(.+\\))(\\*(\\(.+\\)))+\\)","$3");
				v.add(parse(last));
				s = "("+s.replaceAll("\\((\\(.+\\))(\\*(\\(.+\\)))+\\)","$1")+")";
			}
			
			v.add(parse(s.substring(1,s.length()-1)));
			
			Expression[] factors = new Expression[v.size()];
			for(int i=v.size()-1;i>=0;i--)
				factors[i]=(Expression)v.get(i);
			
			return new Times(factors);
		}
		
		if(s.matches("\\(\\w+\\)")) {
			// Symbol
			return new Symbol(s.replaceAll("\\((\\w+)\\)", "$1"));
		}
		
		if(s.matches("\\(S\\((.+)\\)\\)")) {
			// Simplify  "\\(D\\(\\(.+\\),\\(.+\\)\\)"
			return new Simplify(parse(s.replaceAll("\\(S\\((.+)\\)\\)","$1")));
		}

		
		throw new InvalidExpressionException(s);
	}
	
	public Expression nextExpression() throws IOException, InvalidExpressionException {
		
		String l = br.readLine();
		
		if(l==null) return null;
		else return parse(l);		
	}
	
	public void close() throws IOException {
		br.close();
		fr.close();
	}
	
	public Iterator iterator() throws IOException, InvalidExpressionException {
		Vector v = new Vector();
		Expression e;
		while((e=this.nextExpression())!=null)
			v.add(e);
		
		this.close();
		return v.iterator();
	}
}