java 8 lambdas interface mismatch

Asked Sep 18 '17 at 20:52

Active Sep 18 '17 at 21:07

Viewed 45 times

I have an interface with following code

public interface DoSomething {
    public void blah(String s);
}

Next, i have a class which uses this interface as shown below

public class Dummy {
 public static void main(String[] args) {
    //how is the below working when String's equalsIgnoreCase method signature does not match the signature of my interface DoSomething
    String s = "Jim";
    doSomething(s::equalsIgnoreCase, "jim");
  //Again signature mismatch, but code compiles fine
    doSomething(String::toUpperCase, "jim");

 }
 public static void doSomething(DoSomething x, String s) {
    x.blah(s);
 }
}

asked Sep 18 '17 at 20:52

Jimm

8,165
16
69
118

What part of the method signatures do you think don't match? The return type? – Sotirios Delimanolis Sep 18 '17 at 21:01
[I have run your program](https://ideone.com/8rbXAT) and works ok. Please add your log. – Juan Carlos Mendoza Sep 18 '17 at 21:01
He is wondering why it works, not why it not works. – UninformedUser Sep 18 '17 at 21:03
2

@SotiriosDelimanolis I think the OP is asking why he can pass `s::equalsIgnoreCase` or `String::toUpperCase` as the first parameter to `doSomething`. – GriffeyDog Sep 18 '17 at 21:03
@GriffeyDog Right. Why do they think they shouldn't be able to? – Sotirios Delimanolis Sep 18 '17 at 21:06
@SotiriosDelimanolis my interface returns void, where as string's equalIgnoreCase returns a boolean and toUpperCase returns a String – Jimm Sep 18 '17 at 21:08
That's what I thought. See the duplicate. – Sotirios Delimanolis Sep 18 '17 at 21:09

java 8 lambdas interface mismatch

0 Answers0