基于lambda嵌套列表的过滤列表

Question

我有一个类似这样的组对象

public class Group { 
    private String mName;
    private List<Item> mItems;
}

和如下所示的Item对象

public class Item {
    private String mNumber;
}

firstList.stream()
.flatMap(group -> group.getItemList().stream())
.filter(item -> (
        // here I'm stuck. I think i need a stream of the second list or something?
        ))
.collect(Collectors.toList());

Answer 1

lastlist不包含

firstList.stream()
.flatMap(group -> group.getItemList().stream())
.filter(item -> (!lastList.countains(item)))
.collect(Collectors.toList());