How is a getter method of a class a Function<ThisObject, ReturnType> if a getter doesn't take in anything?

https://medium.com/quick-code/java-8-functional-programming-how-i-do-f11239a0aa90

I'm looking at this article because I was wondering how to implement getters in functional interfaces for long xml-type nested objects (basically trying to figure out if I can chain getters to get a deeply nested object that represents an XML tree).

The part that confuses me is how a getter is a Function<City, String>. Do non static methods always take in the object that the method corresponds to? I've read a lot of the docs but I don't see any of this mentioned. Can someone point me in the right direction here?

Why City::getName not supplier? Getters don't take in anything.

Solution

If you want to express City::getName, the lambda could also be written accordingly, maybe makes it more concise to understand what exactly happens:

final Function<City, String> getPrice = c -> c.getName();

Additional to the discussion, why is it a Function and not a Supplier: In contrast to the Supplier, the Function takes an argument. So the use-case would be different.

With Supplier, you would always base on the same City, eg.

 final City city = currentCity
 supplier = () -> city.getName()
 // or
 supplier = city::getName

With Function<City,String>, you would always provide the instance to the Function:
```
 func = (city) -> city.getName()
 // or
 func = City::getName
```