default-method

问题 I have a class A in java and interface B in Kotlin. // kotlin interface B { fun optional() } // java class A implements B { } I want to write the default method (Java 8 feature) in Kotlin interface (B) and want to implement it in the class A. How can I achieve it? Thanks in advance. 回答1: In Kotlin, interface methods with bodies are by default compiled as following: // kotlin interface B { fun optional() { println("B optional body") } } is compiled roughly to: public interface B { void

问题 As per the Interface Segregation Principle clients should not be forced to implement the unwanted methods of an interface ...and so we should define interfaces to have logical separation. But default methods introduced in Java 8 have provided the flexibility to implement methods in Java interfaces. It seems Java 8 has provided the feasibility to enhance an interface to have some methods not related to its core logic, but with some default or empty implementation. Does it not violate the ISP?

问题 As per the Interface Segregation Principle clients should not be forced to implement the unwanted methods of an interface ...and so we should define interfaces to have logical separation. But default methods introduced in Java 8 have provided the flexibility to implement methods in Java interfaces. It seems Java 8 has provided the feasibility to enhance an interface to have some methods not related to its core logic, but with some default or empty implementation. Does it not violate the ISP?

问题 Learning java 8 default methods . This link like any other resource on internet says In ‘the strictest sense’, Default methods are a step backwards because they allow you to ‘pollute’ your interfaces with code. But they provide the most elegant and practical way to allow backwards compatibility. It made it much easier for Oracle to update all the Collections classes and for you to retrofit your existing code for Lambda. My understanding is that java 8 dev/designers provided the default method

问题 Java 8 introduces default methods to provide the ability to extend interfaces without the need to modify existing implementations. I wonder if it's possible to explicitly invoke the default implementation of a method when that method has been overridden or is not available because of conflicting default implementations in different interfaces. interface A { default void foo() { System.out.println("A.foo"); } } class B implements A { @Override public void foo() { System.out.println("B.foo"); }

问题 I came across following paragraph while reading about java 8 default methods from here: If any class in the hierarchy has a method with same signature, then default methods become irrelevant. A default method cannot override a method from java.lang.Object. The reasoning is very simple, it’s because Object is the base class for all the java classes. So even if we have Object class methods defined as default methods in interfaces, it will be useless because Object class method will always be

问题 Consider the below example, public class Testing extends SupCls implements Intf { public static void main(String[] args) { new Testing().test(); } } class SupCls { public void test() { System.out.println("From SupCls"); } } interface Intf { public default void test() { System.out.println("From Intf"); } } As you can see, there's no connection between SupCls class and Intf interface. But both are defining a common method. And Testing class is extending SupCls and implementing Intf . So, when I

问题 This question already has answers here : Explicitly calling a default method in Java (4 answers) Closed 5 years ago . Say I have two classes, A and B : class A { void method() { System.out.println("a.method"); } } class B extends A { @Override void method() { System.out.println("b.method"); } } After instantiating B as b , I can call B 's method like b.method() . I can also make B 's method call A 's method with super.method() . But what if A is an interface: interface A { default void method

问题 I often want to map one list into another list. For example if I had a list of people, and I wanted a list of their names, I would like to do: GOAL List<Person> people = ... ; List<String> names = people.map(x -> x.getName()); Something like this is possible with Java 8: JAVA 8 VERSION List<String> names = people.stream() .map(x -> x.getName()) .collect(Collectors.toList()); But this is clearly not as nice. In fact, I think using Guava is cleaner: GUAVA VERSION List<String> names = Lists

问题 Lets say I have the following structure: abstract class A { abstract boolean foo(); } interface B { default boolean foo() { return doBlah(); } } class C extends A implements B { //function foo } Java will now complain that class C must implement abstract method foo from A . I can work around this problem relatively easy by redefining the function in C and simply calling B.super.foo(); . however I do not understand why the default function from interface B does not forfill this requirement on