import java.util.function.Supplier;
import org.junit.Test;

public class GenericsTest {

    @Test
    public void testObjectSupplier() {
        Supplier<Object> objectSupplier = () -> "Object";
        Supplier<String> stringSupplier = () -> "String";

        object(objectSupplier);
        //object(stringSupplier); // Uncommenting leads to compile failure

        //string(objectSupplier); // Uncommenting leads to compile failure
        string(stringSupplier);

        extendsObject(objectSupplier); // Works fine
        extendsObject(stringSupplier); // Works fine
    }

    private void object(Supplier<Object> objectSupplier) {
        System.out.println("object: "+objectSupplier.get());
    }

    private void string(Supplier<String> stringSupplier) {
        System.out.println("string: "+stringSupplier.get());
    }

    private void extendsObject(Supplier<?> extendsObjectSupplier) {
        System.out.println("extends object: "+extendsObjectSupplier.get());
    }
}