In the book Saturday Night and Sunday Morning by Alan Sillitoe, is Arthur an idealist or a materialist?

Arthur is an injured idealist who hides his disappointment in materialism and sensualism. When he is passing the factory where he works, he thinks to himself,

"With the wages...you could go on a ten-day binge and get rid of all you'd saved. Because it was no use saving your money year after year. A mug's game, since the value of it got less and less and you never knew when the Yanks were going to do something daft like dropping the H-bomb on Moscow" (page 23).

He is not a materialist because he does not save the wages he earns or spend them on anything other than getting drunk and being with Brenda and Winnie, two sisters, both married, with whom he is having adulterous and disastrous affairs. His idealism is tarnished by a deep sense of nihilism, or believing in nothing, which he reveals in the quote above. His crushed sense of idealism comes from living in a world in which destruction from the H-bomb can be immediate and in which his work in the factory is soul-crushing. Nonetheless, a sense of idealism lives within him. 

His life is literally divided between Saturday night, when he carouses and has illicit affairs, and Sunday morning, when he deals with the aftermath of his carousing. After the husband of one of the women he is cheating with beats him up, he eventually has a conversion to a more idealistic and committed life. He realizes that he should commit himself to Doreen, a nineteen-year-old who refuses to become involved with him unless he is serious. “He should have kept to the safe and rosy path with Doreen" (page 166), he thinks. In the end, he has an idealistic notion of his commitment to Doreen and promises to take care of her, showing that he is ultimately idealistic if he has something or someone to commit himself to.