inner-classes

问题 I was reading Effective Java 2 - Item 22 and it says in the title: "Favor static member classes over non-static" but at the end of the chapter Implementations of the collection interfaces, such as Set and List, typically use nonstatic member classes to implement their iterators: // Typical use of a nonstatic member class public class MySet<E> extends AbstractSet<E> { ... // Bulk of the class omitted public Iterator<E> iterator() { return new MyIterator(); } private class MyIterator implements

问题 public class Test { public static void main(String[] args) { } } class Outer { void aMethod() { class MethodLocalInner { void bMethod() { System.out.println("Inside method-local bMethod"); } } } } Can someone tell me how to print the message from bMethod ? 回答1: You can only instantiate MethodLocalInner within aMethod . So do void aMethod() { class MethodLocalInner { void bMethod() { System.out.println("Inside method-local bMethod"); } } MethodLocalInner foo = new MethodLocalInner(); //

问题 So I was having a bug where my code was crashing because I am calling methods in my outer class in onPostExecute . So this is my simple class: public class UsersList extends Fragment{ @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { ... } public void callMe(){ Toast.makeText(getContext(), "I work", Toast.LENGTH_LONG).show(); } public class UserRecommend extends AsyncTask<String, String, String> { @Override protected String

问题 I have a template class. It has a template function. Both take different template parameters. There is an internal class that needs to make a friend of the enclosing class's template function. Compiler errors abound. The following toy example shows my issue. First, the following of course compiles (VS 2017): template <typename T> class Class1 { public: Class1() = default; ~Class1() = default; template <typename U> void Func(U& x) {}; }; class Class2 { public: Class2() = default; ~Class2() =

问题 I have following test: @RunWith(Enclosed.class) public class ProductTest { @RunWith(MockitoJUnitRunner.class) @Ignore public static abstract class Base1 { @Before public void setUpBase() {...} } public static class Test1 extends Base1{ @Test public void foo(){...} } } public static class Test2 extends Base1{ @Test public void bar(){...} } } } To avoid @Ignore I refactored class like this: @RunWith(Enclosed.class) public class ProductTest { @RunWith(MockitoJUnitRunner.class) public static

问题 So I have a tree class: public class Tree<T> : IEnumerable where T : IComparable<T> { private Node<T> root = null; ... private class Node<T> : IEnumerable<T> where T : IComparable<T> { private Node<T> left, right; ... } } It works fine, but I get the compiler warning: Type parameter 'T' has the same name as the type parameter from outer type 'Tree<T>' Well, of course it's the same name, they should be the same type. (In fact, since the Node class is private and thus can never be accessed

问题 I know the concept of singleton in Java. I'm having problems with creating singleton as inner class in Java. Problem occurs at holder's public class NormalClass { private class Singleton { private static Singleton instance = null; private Singleton() { } private static class SingletonHolder { private static Singleton sessionData = new Singleton(); } public static Singleton getInstance() { return NormalClass.Singleton.SingletonHolder.sessionData; } } public void method1() { Singleton

问题 I can extend an inner class/trait inside the outer class or inside a class derived from the outer class. I can extend an inner class of a specific instance of an outer class as in: class Outer { class Inner{} } class OtherCl(val outer1: Outer) { class InnA extends outer1.Inner{} } Note: even this seems to compile fine producing very interesting possibilities: trait OuterA { trait InnerA } trait OuterB { trait InnerB } class class2(val outerA1: OuterA, val outerB1: OuterB) { class Inner2

问题 I'm trying access to a static inner class method, but I can't find the right way. I need to write this java code in Clojure: SessionProperties sessionProperties = SessionProperties.Builder().mediaMode(MediaMode.ROUTED).build(); My code is: (:import [com.opentok OpenTok MediaMode SessionProperties SessionProperties$Builder])) (def sessionProperties (.build (.mediaMode SessionProperties$Builder MediaMode/ROUTED)) And this is the error: java.lang.IllegalArgumentException: No matching method

问题 I'm having difficulty defining and specializing a member function update() of an inner class Outer<T1>::Inner that is templated on a non-type (enum) argument. #include <cstdlib> template<typename T1> struct Outer { struct Inner { enum Type{ A , B , C }; template<Type T2> void update(); }; }; // Definition template<typename T1> template<Outer<T1>::Inner::Type T2> void Outer<T1>::Inner::update() { } // Specialization template<typename T1> template<Outer<T1>::Inner::A > void Outer<T1>::Inner: