public String equals(){
        if(operator == null){
            return this.numberBuffer;
        }else{
            float operand = Float.parseFloat(this.numberBuffer);
            this.operand2 = operand;
            float cal = 0;
 
            // +, -, *, / requires two operands
            if(operator.equals("+")){
                cal = this.operand1 + this.operand2;
            }
            if(operator.equals("+")){
                cal = this.operand1 + this.operand2;
            }
            if(operator.equals("-")){
                cal = this.operand1 - this.operand2;
            }
            if(operator.equals("*")){
                cal = this.operand1 * this.operand2;
            }
            if(operator.equals("\u00F7")){
                if(this.operand2 == 0){
                    return "Error";
                }
                cal = this.operand1 / this.operand2;
            }
            this.numberBuffer = Float.toString(cal);
            this.isResult = true;
            this.afterEql = true;
            return Float.toString(cal);
        }
    }