Cannot infer functional interface type Java 8

I have a factory(Registry DP) which initializes the class:

public class GenericFactory extends AbstractFactory { public GenericPostProcessorFactory() { factory.put("Test", defaultSupplier(() -> new Test())); factory.put("TestWithArgs", defaultSupplier(() -> new TestWithArgs(2,4))); } } interface Validation Test implements Validation TestWithArgs implements Validation 

And in the AbstractFactory

 protected Supplier<Validation> defaultSupplier(Class<? extends Validation> validationClass) { return () -> { try { return validationClass.newInstance(); } catch (InstantiationException | IllegalAccessException e) { throw new RuntimeException("Unable to create instance of " + validationClass, e); } }; } 

But I keep getting Cannot infer functional interface type Error. What I am doing wrong here ?

1 Answer

Your defaultSupplier method has an argument type of Class. You can’t pass a lambda expression where a Class is expected. But you don’t need that method defaultSupplier anyway.

Since Test and TestWithArgs are a subtypes of Validation, the lambda expressions () -> new Test() and () -> new TestWithArgs(2,4) are already assignable to Supplier<Validation> without that method:

public class GenericFactory extends AbstractFactory { public GenericPostProcessorFactory() { factory.put("Test", () -> new Test()); factory.put("TestWithArgs", () -> new TestWithArgs(2,4)); } }