private double parseBracket() throws Exception{
		double result; //   
	    // ǰΪţʾһ  
	    if (this.token.equals("(")) {  
	    	this.getToken(); // ȡһ  
	        result = this.parseAddOrSub();// üӼӱʽֵ  
	        // ǰǲţ׳Ųƥ쳣  
	        if (!this.token.equals(")")){  
	            this.handleError(UNBALPARENS_ERROR);  
	        }  
	        this.getToken(); // ȡһ  
	    } else {  
	        // ǲţʾһ㣬ԭԪӱʽֵ  
	        result = this.parseAtomElement();  
	    }  
	    return result;
	}