default-method

问题 I have to design an interface for hierarchical entity: interface HierarchicalEntity<T extends HierarchicalEntity<T>> { T getParent(); Stream<T> getAncestors(); } It's quite easy to implement default getAncestors() method in terms of getParent() in such a way that the former would return Stream of all the ancestors. Implementation example: default Stream<T> getAncestors() { Stream.Builder<T> parentsBuilder = Stream.builder(); T parent = getParent(); while (parent != null) { parentsBuilder.add

问题 I have to design an interface for hierarchical entity: interface HierarchicalEntity<T extends HierarchicalEntity<T>> { T getParent(); Stream<T> getAncestors(); } It's quite easy to implement default getAncestors() method in terms of getParent() in such a way that the former would return Stream of all the ancestors. Implementation example: default Stream<T> getAncestors() { Stream.Builder<T> parentsBuilder = Stream.builder(); T parent = getParent(); while (parent != null) { parentsBuilder.add

问题 I was reading this tutorial on Java 8 where the writer showed the code: interface Formula { double calculate(int a); default double sqrt(int a) { return Math.sqrt(a); } } And then said Default methods cannot be accessed from within lambda expressions. The following code does not compile: Formula formula = (a) -> sqrt( a * 100); But he did not explain why it is not possible. I ran the code, and it gave an error, incompatible types: Formula is not a functional interface` So why is it not

问题 Since Java 8 interfaces could have default methods. I know how to invoke the method explicitly from the implementing method, i.e. (see Explicitly calling a default method in Java) But how do I explicitly invoke the default method using reflection for example on a proxy? Example: interface ExampleMixin { String getText(); default void printInfo(){ System.out.println(getText()); } } class Example { public static void main(String... args) throws Exception { Object target = new Object(); Map

问题 Since Java 8 interfaces could have default methods. I know how to invoke the method explicitly from the implementing method, i.e. (see Explicitly calling a default method in Java) But how do I explicitly invoke the default method using reflection for example on a proxy? Example: interface ExampleMixin { String getText(); default void printInfo(){ System.out.println(getText()); } } class Example { public static void main(String... args) throws Exception { Object target = new Object(); Map

问题 In my application I run into a problem that when a getter in a class is defaulted in an interface only (Java 8 feature), there is no Java Beans property as a result. I.e. for normal method invocation it works just as a standard method, but for access through "properties" it suddenly behaves differently... Here is a test case: import java.beans.Introspector; import java.util.Arrays; import java.util.stream.Collectors; import org.apache.commons.beanutils.PropertyUtils; public class test {

问题 It has generally been the case the Java source code has been forward compatible. Until Java 8, as far as I know, both compiled classes and source have been forward compatible with later JDK/JVM releases. [Update: this is not correct, see comments re 'enum', etc, below.] However, with the addition of default methods in Java 8 this appears to no longer be the case. For example, a library I have been using has an implementation of java.util.List which includes a List<V> sort() . This 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 have very few knowledges in java so I maybe misunderstood my problem: I'm working on the Gephi API which is in Java, and I used IKVMC to work on a dll. I tried to create an empty graph as explained here in the Gephi doc https://github.com/gephi/gephi/wiki/How-to-manipulate-Graph In C# I tried this: ProjectController pc; pc = (ProjectController)org.openide.util.Lookup.getDefault().lookup(typeof(ProjectController)); At the second line I get the following error: Exception non gérée : System

问题 Does Java have plan that default method substitute for Abstract Class ? I could not find a real case to use default method instead of Abstract? 回答1: Default methods can't substitute abstract classes, as abstract classes can (and often do) have fields. Interfaces can only contain behaviour and not state, which is unlikely to change in the future as multiple inheritance of state in Java is seen (rightly or wrongly) as evil. They can also have final methods, which is another thing you can't