functional-interface

问题 As per the Documentation, Method Reference is absolutely not a static call. It works on both static and non- static methods. When we define our own non-static method in a given class and try to use it using Method Reference then the compile-time-error "cannot make static reference to non static method" is NOT seen in case of Function but only seen in case of Supplier, Consumer and Predicate. Why is that so? class Demo{ private Function<Student, Integer> p= Student::getGradeLevel; // fine

问题 As per the Documentation, Method Reference is absolutely not a static call. It works on both static and non- static methods. When we define our own non-static method in a given class and try to use it using Method Reference then the compile-time-error "cannot make static reference to non static method" is NOT seen in case of Function but only seen in case of Supplier, Consumer and Predicate. Why is that so? class Demo{ private Function<Student, Integer> p= Student::getGradeLevel; // fine

问题 The Callable and Supplier functional interfaces in java.util.concurrent and java.util.function packages respectively have the following signature- public interface Callable<V> { V call() throws Exception; } public interface Supplier<T> { T get(); } Are there some specific use case where each one of them fit more than the other? 回答1: Their difference in usage can be seen from their respective documentation: Callable: A task that returns a result and may throw an exception . Implementors define

问题 The Callable and Supplier functional interfaces in java.util.concurrent and java.util.function packages respectively have the following signature- public interface Callable<V> { V call() throws Exception; } public interface Supplier<T> { T get(); } Are there some specific use case where each one of them fit more than the other? 回答1: Their difference in usage can be seen from their respective documentation: Callable: A task that returns a result and may throw an exception . Implementors define

问题 Please consider this example: import java.util.function.Consumer; public class Example { public static void main(String[] args) { Example example = new Example(); example.setConsumer(test -> System.out.println("passed string is " + test)); //uses MyConsumer, why ? example.getConsumer().accept("Test 1"); example.setConsumer((MyConsumer<String>)test -> System.out.println("passed string is " + test)); //uses MyConsumer example.getConsumer().accept("Test 2"); example.setConsumer((Consumer<String>

问题 Please consider this example: import java.util.function.Consumer; public class Example { public static void main(String[] args) { Example example = new Example(); example.setConsumer(test -> System.out.println("passed string is " + test)); //uses MyConsumer, why ? example.getConsumer().accept("Test 1"); example.setConsumer((MyConsumer<String>)test -> System.out.println("passed string is " + test)); //uses MyConsumer example.getConsumer().accept("Test 2"); example.setConsumer((Consumer<String>

来源： https://stackoverflow.com/questions/58133360/why-does-functional-interface-with-void-return-type-method-accept-any-return-typ

问题 Why does the below code return Predicate<String> and not boolean ? My understanding is that the !s.isEmpty() check here is going against the Predicate boolean test(T t); The return type here is boolean . So in my lambda should my nonEmptyStringPredicate not be of type boolean ? Obviously, it's not, I'm just trying to understand why it's not. Predicate<String> nonEmptyStringPredicate = (String s) -> !s.isEmpty(); 回答1: A Predicate gets in this case a String as parameter and returns a boolean .

问题 Why does the below code return Predicate<String> and not boolean ? My understanding is that the !s.isEmpty() check here is going against the Predicate boolean test(T t); The return type here is boolean . So in my lambda should my nonEmptyStringPredicate not be of type boolean ? Obviously, it's not, I'm just trying to understand why it's not. Predicate<String> nonEmptyStringPredicate = (String s) -> !s.isEmpty(); 回答1: A Predicate gets in this case a String as parameter and returns a boolean .

问题 I am trying to write a method that can take in a String classname and a String value, and return the value represented as that String. Example inputs: parse("java.lang.String", "abc") -> String "ABC" parse("java.lang.Boolean", "FALSE") -> Boolean FALSE parse("java.lang.Integer", "123") -> Integer 123 parse("com.me.Color", "RED") -> enum Color.RED I have found that if I use an if block containing assignableFrom calls, I can achieve this. But would prefer writing something more extendable, so