多线λ比较器 [英] Multiline lambda comparator

问题描述

我从Java中的lambda表达式开始，我认为有些奇怪，并且我确定自己做错了什么，或者有解决方法.

I am starting with the lambda expressions in Java and there is something that I consider bizarre and I am sure that I am doing something wrong or it has a workaround.

要定义比较器，我可以这样做:

To define a comparator, I can do:

 col.setComparator((CustomCell o1, CustomCell o2) ->
            ((Comparable) o1.getValue()).compareTo(o2.getValue())
        );

但是，如果我仅添加两个"{"，哪个很棒.我收到编译错误:

Which is great, however, if I just add two "{". I get a compilation error:

 col.setComparator((CustomCell o1, CustomCell o2) -> {
            ((Comparable) o1.getValue()).compareTo(o2.getValue());
        });

该错误与"{"无关，但与setComparator有关:

The error is not related to the "{", but to setComparator:

The method setComparator(Comparator<CustomCell>) in the type 
TableColumnBase<CustomParentCell,CustomCell> is not applicable for the arguments 
((CustomCell o1, CustomCell o2) -> {})

我之前曾尝试将multiline语句用于actionevents，但它确实起作用:

I have tried using the multiline statements before for actionevents and it does work:

 setOnAction(event -> {
        // do something
 });

是因为它只有一个参数吗?

Is it because it only has one argument?

推荐答案

您正在使用setOnAction实现的方法是

The method you are implementing with setOnAction is

public void handleEvent(ActionEvent event) ;

返回类型为void:即不返回任何内容:

It has a return type of void: i.e. it doesn't return anything:

您正在使用setComparator实现的方法是

The method you are implementing with setComparator is

public int compare(CustomCell cell1, CustomCell cell2) ;

，它返回一个值.要使用更长的格式，对于返回值的方法，您必须具有显式的return语句:

which returns a value. To use the longer form, you must have an explicit return statement for methods that return a value:

col.setComparator((CustomCell o1, CustomCell o2) -> {
        return ((Comparable) o1.getValue()).compareTo(o2.getValue());
    });

这篇关于多线λ比较器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！