public int getPrecedence() {
        if(this instanceof AddOp) {
            return 1;
        } else if(this instanceof SubOp) {
            return 1;
        } else if(this instanceof MulOp) {
            return 2;
        } else if(this instanceof DivOp) {
            return 2;
        } else if(this instanceof EqualOp) {
            return 0;
        }
        return -1;
    }