Suppose we have a default method in a interface,
in implementing class if we need to add some additional logic besides the one the default method already does we have to copy the whole method? is there any possibility to reuse default method... like we do with abstract class
super.method()
// then our stuff...
You can invoke it like this:
interface Test {
public default void method() {
System.out.println("Default method called");
}
}
class TestImpl implements Test {
#Override
public void method() {
Test.super.method();
// Class specific logic here.
}
}
This way, you can easily decide which interface default method to invoke, by qualifying super with the interface name:
class TestImpl implements A, B {
#Override
public void method() {
A.super.method(); // Call interface A method
B.super.method(); // Call interface B method
}
}
This is the case why super.method() won't work. As it would be ambiguous call in case the class implements multiple interfaces.
Related
An experimental/theoretical question concerning any OOP language (Java, C#, Typescript, etc..)
Usually, when implementing an interface in a class, one has to override all the functions of that interface in the class by having to write the code for each function from that interface. And every class that implements this interface has to have its own code for those functions. Suppose we have an interface called Test that has a function called foo() in which I want the following code System.out.println("This is an interface function");.Usually one has to make an interface and declare the function and then writes the code in every implementing class
But what if there is some "theoretical" way of having all of the function written in the interface and every implementing class can just call it without having to override. Something like the following (using Java as a base language):
interface Test {
public foo() {
System.out.println("Test log.")
}
}
class Class1 implements Test {
constructor() {}
}
class Class2 implements Test {
constructor() {}
}
class Main {
public static void main() {
Class1 f1 = new Class1();
Class2 f2 = new Class2();
f1.foo();
f2.foo();
}
}
Java has this feature since Java 8. Interfaces can have default implementations where the class is free to override them, but not required to do so.
interface Test {
default void foo() {
System.out.println("Test log.");
}
}
First of all, this is not a duplicate of Spring Data: Override save method. I want to override the save method, and I know where to find the documentation, but my question is how to call the original implementation in my custom code.
To override save() method in spring-data-*, you do something like below:
interface CustomizedSave<T> {
<S extends T> S save(S entity);
}
class CustomizedSaveImpl<T> implements CustomizedSave<T> {
public <S extends T> S save(S entity) {
// Your custom implementation
}
}
interface UserRepository extends CrudRepository<User, Long>, CustomizedSave<User> {
}
interface PersonRepository extends CrudRepository<Person, Long>, CustomizedSave<Person> {
}
My question is how to call the "super" implementation of save()? In spring-data-elasticsearch, the default save() implementation is not so simple to set up (basically I need to copy AbstractElasticsearchRepository source code), so I would rather not do this.
#Autowired
private EntityManager em;
#Override
public User save(User entity) {
JpaRepositoryFactory jrf = new JpaRepositoryFactory(em);
UserRepositories repoWithoutCustom = jrf.getRepository(UserRepositories.class);
do somth....
}
Where repoWithoutCustom what you need, your UserRepository without any customized methods. Just use required RepositoryFactory, in your case Elastic as i understood
As mention here: if a function in an interface has no body it is abstract by default. But there is nothing about interface's function with body.
Example:
interface MyInterface {
fun foo() { print("Something") }
fun bar()
}
fun main(args: Array<String>) {
println(MyInterface::foo.javaMethod)
println(MyInterface::bar.javaMethod)
}
Output will be:
public abstract void MyInterface.foo()
public abstract void MyInterface.bar()
How it's possible, that method with defined body is abstract?
This has to do with the way default methods in Kotlin interfaces are implemented. The foo and bar methods in your interface really are both abstract.
However, there is an inner class inside the interface that looks something like this (simplified):
public interface MyInterface {
void foo();
void bar();
public static final class DefaultImpls {
public static void foo() {
System.out.print("Something");
}
}
}
This class is the one that contains the default implementations of any functions that you gave a body to inside the interface.
Then, if you create a class that implements this interface, and you don't override the foo method:
class MyClass: MyInterface {
override fun bar() {
println("MyClass")
}
}
Then you get one generated automatically, which just calls the implementation inside DefaultImpls:
public final class MyClass implements MyInterface {
public void bar() {
System.out.println("MyClass");
}
public void foo() {
MyInterface.DefaultImpls.foo();
}
}
You can find all these details by using the bytecode viewer that comes with the Kotlin plugin (Tools -> Kotlin -> Show Kotlin Bytecode, and then the Decompile option).
I had following code
public interface IFoo
{
void Execute();
}
public abstract class FooBar: IFoo
{
public void Execute()
{
OnExecute();
}
public abstract void OnExecute();
}
and following test case to test the Execute() method
[Fact]
public void When_execute_method_called_Expect_executionTime_is_set()
{
var sutMethod = A.Fake<FooBar>();
A.CallTo(sutMethod).
Where(x => x.Method.Name == "OnExecute").
Invokes(x => Thread.Sleep(100)));
sutMethod.Execute();
Assert.NotEqual(0, sutMethod.Result.ExecutionTime.Ticks);
}
sutMethod.Execute(); call would go to FooBar.Execute()
later I decided to make the interface into an abstract class
public abstract class IFoo
{
public abstract void Execute();
}
public abstract class FooBar:IFoo
{
public override void Execute()
{
OnExecute();
}
public abstract void OnExecute();
}
Now sutMethod.Execute(); call does not invoke FooBar.Execute()
I thought FakeItEasy would handles interface and abstract classes as equal.What am I missing?
Update
# Blair Conrad provided the reasoning for the behaviour
Is it possible to make minimal changes to the test case to get the original behaviour back?
thanks
The difference is due to the overrideability of the method Execute on FooBar.
FakeItEasy can only override virtual members, abstract members, or interface members.
In your original example, when IFooBar is an interface and FooBar implements it, Execute is a concrete method. It's not virtual, nor is it abstract. Thus FakeItEasy can't intercept calls to it, and the original method is executed.
Once you change IFooBar to an abstract class, you have an abstract IFooBar.Execute, which you override in FooBar. As such, FooBar.Execute is now virtual and can be intercepted by FakeItEasy. Which it does, so your implementation is not called.
Following addition help solve the issue
A.CallTo(() => sutMethod.Execute()).CallsBaseMethod();
This calls the virtual method Executeof FooBar
i was recently digging on new partial methods in c#3.0, i understood the use of partial class, that it could be chunked into multiple file one contain the definition and other declaration, but i wanted to know,i created a partial class like below:
in class1.cs
partial class A
{
partial void Method();
}
in class2.cs
partial class A
{
partial void Method()
{
Console.WriteLine("Hello World");
}
}
now in class3.cs
class MainClass
{
static void Main()
{
A obj = new A();
obj.Method(); //Here i cannot call the "Method" method.
}
}
then whats the use of creating partial method, i read on MSDN that, at runtime, compiler compiles the class into one, in that case compiler should be getting the "Method" method implementation also, then why it dont allow me to call the "Method" method in the main method, can anyone correct me if i am wrong, and tell me why i am unable to call this partial method in main.
From MSDN
No access modifiers or attributes are allowed. Partial methods are
implicitly private.
It's a private method, so you can't call it from main.
You can call a partial method inside the constructor where the method is defined.
For example
public partial class classA
{
partial void mymethod();
}
public partial class classA
{
partial void mymethod()
{
Console.WriteLine("Invoking partial method");
}
public ClassA()
{
mymethod();
}
}
public class MainClass
{
static void Main()
{
ClassA ca=new ClassA();
}
}
That's it..now execute your code and see the result..
OutPut
Invoking partial method
Yes, we can't call it from Main(). Problem is not Partial method problem is method without specifier in a class is Private and private method can be called inside the class only.
Try creating a new public method in Partial class:
partial class A
{
partial void Method();
}
partial class A
{
partial void Method()
{
Console.WriteLine("Hello World");
}
public void Study()
{
Console.WriteLine("I am studying");
Method();
}
}
class MainClass
{
static void Main()
{
A obj = new A();
obj.Study();
}
}