用Java编写C＃委托 [英] Write C# delegate in java

问题描述

如何在下面的Java版本中编写代码？

How can I write code below in java version?

我读过类似的问题，但是它们令人困惑，他们回答说Java没有像这样的委托功能。另一方面，C＃用Java中的委托实现进行了回答，但是与我的情况没有什么相似之处。
我真的希望这个问题清楚。
一个星期以来我一直被困住

I have read similar questions, but they are confusing, they answered that java didn't have delegate feature like c# had, in other hand they answered with their delegate implementation in java, but nothing is similar with my condition. I really hope it's clear on this question. I have been getting stuck since a week

    class Action
    {
        public delegate void ActionDelegate();
        public static ActionDelegate OnAction;

        public void DoAction()
        {
            Console.WriteLine("Action A");
            if (!ReferenceEquals(OnAction, null))
                OnAction();
        }
    }
    class TaskA
    {
        public TaskA()
        {
            Action.OnAction += DoTaskA;
        }
        private void DoTaskA()
        {
            Console.WriteLine("Do Task A");
        }

    }
    class TaskB
    {
        public TaskB()
        {
            Action.OnAction += DoTaskB;
        }
        private void DoTaskB()
        {
            Console.WriteLine("Do Task B");
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            TaskA taskA = new TaskA();
            TaskB task = new TaskB();
            Action action = new Action();
            action.DoAction();
        }
    }

输出：

Action A
Do Task A
Do Task B
Press any keys to continue...

推荐答案

使用项目安全镜在您的类路径中，您将获得对代表和事件的库支持。

With the project safety-mirror on your classpath your get library support for delegates and events.

<dependency>
    <groupId>com.github.hervian</groupId>
    <artifactId>safety-mirror</artifactId>
    <version>3.0.0</version>
</dependency>

这里是项目自述文件：

• 乐趣和朋友：没有更多的功能接口：
  
  Fun.With0Params< String> myFunctionField =" hello world :: trim;

Fun.With2Params< Boolean，Object，Object> equals = Objects :: equals;

  public void foo(Fun.With1ParamAndVoid<String> printer) throws Exception {
      printer.invoke("hello world);
  }  
  foo(System.out::println);   //This signature match the the Fun defined by method Foo. If it did not, the compiler would emit an error.  

这都是类型安全的：如果方法引用的签名不符合函数引用的定义，则会出现编译时错误。 Fun子类。

It is all type safe: you will get compile time errors if the Method Reference's signature does not match what is defined by the Fun subclass.

  Method m1 = Fun.toMethod(String::isEmpty)
  Method m2 = Fun.<String>toMethod(Class::forName)); // to get overloaded method you must specify parameters in generics  

  assertEquals("isEmpty", Fun.getName(String::isEmpty)); //use Fun's static getName method to get the method name. The Method objects returned from toMethod will not return the correct String.

Java中的代表！

Delegates in Java!

  Delegate.With1Param<String, String> greetingsDelegate = new Delegate.With1Param<>();
  greetingsDelegate.add(str -> "Hello " + str);
  greetingsDelegate.add(str -> "Goodbye " + str);

  DelegateInvocationResult<String> invocationResult = greetingsDelegate.invokeAndAggregateExceptions("Sir");

  invocationResult.getFunctionInvocationResults().forEach(funInvRes -> System.out.println(funInvRes.getResult()));
  //prints: "Hello sir" and "Goodbye Sir"

事件

Events

  //Create a private Delegate. Make sure it is private so only *you* can invoke it.
  private static Delegate.With0Params<String> trimDelegate = new Delegate.With0Params<>();

  //Create a public Event using the delegate you just created.
  public static Event.With0Params<String> trimEvent= new Event.With0Params<>(trimDelegate);

类型安全方法创建

Type safe method creation

  Method m1 = Fun.toMethod(Thread::isAlive)  // Get final method
  Method m2 = Fun.toMethod(String::isEmpty); // Get method from final class
  Method m3 = Fun.toMethod(BufferedReader::readLine); // Get method that throws checked exception
  Method m4 = Fun.<String, Class[]>toMethod(getClass()::getDeclaredMethod); //to get vararg method you must specify parameters in generics
  Method m5 = Fun.<String>toMethod(Class::forName); // to get overloaded method you must specify parameters in generics
  Method m6 = Fun.toMethod(this::toString); //Works with inherited methods

免责声明：我是该项目的作者。

Disclaimer: I am the author of the project.

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