Multiline lambda comparator

Question

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. To define a comparator, I can do: ``` col.setComparator((CustomCell o1, CustomCell o2) -> ((Comparable) o1.getValue()).compareTo(o2.getValue()) ); ``` 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()); }); ``` The error is not related to the "{", but to `setComparator`: ``` The method setComparator(Comparator) in the type TableColumnBase is not applicable for the arguments ((CustomCell o1, CustomCell o2) -> {}) ``` I have tried using the multiline statements before for actionevents and it does work: ``` setOnAction(event -> { // do something }); ``` Is it because it only has one argument?

Accepted Answer

The method you are implementing with `setOnAction` is

```
public void handleEvent(ActionEvent event) ;
```

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

The method you are implementing with `setComparator` is

```
public int compare(CustomCell cell1, CustomCell cell2) ;
```

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());
    });
```

Multiline lambda comparator

Solution

Problem