I did this:
public class LambdaConflict
{
public static void main(String args[]){
//*
System.out.println(LambdaConflict.get(
(str) -> "Hello World!! By ME?"
));
/*/
System.out.println(LambdaConflict.get(new Intf<String> (){
@Override public String get1(String str){
return "Hello World!! By get1 " + str;
}
}));
/*****/
}
public static String get(Intf<String> i, boolean b){
return i.get1("from 1");
}
}
interface Intf<T>
{
public T get1(T arg1);
public T get2(T arg1);
}
and get this exception:
incompatible types: Intf is not a functional interface multiple non-overriding abstract methods found in interface Intf Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output 1 error
Is there any condition that I can't use lambda to replace anonymous class?
Just for reference and to enrich the answers already given:
As per JSR-335: Lambda Expressions for the Java Programming Language, in section Lambda Specification, Part A: Functional Interfaces it says:
A functional interface is an interface that has just one abstract method (aside from the methods of Object), and thus represents a single function contract. (In some cases, this "single" method may take the form of multiple abstract methods with override-equivalent signatures inherited from superinterfaces; in this case, the inherited methods logically represent a single method.)
So, what you need is to either provide a default implementation for one of your methods or put one of your methods in a different interface.
No. There is no way to "overcome" this. A functional interface must have only one abstract method. Your interface has two:
interface Intf<T> {
public T get1(T arg1);
public T get2(T arg1);
}
Note: You don't need to annotate your interface as mentioned in comments. But you can use the @FunctionalInterface
annotation to get compile time errors if your interface is not a valid functional interface. So it brings you a little bit more security in your code.
For more see e.g. http://java.dzone.com/articles/introduction-functional-1
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