Create a custom event in Java

问题:

I want to do something like this in Java but I don\'t know the way:

When event \"object 1 say \'hello\'\" happens, then object 2 responds to that event by saying \"hello\".

Can somebody give me a hint or sample code?

回答1:

You probably want to look into the observer pattern.

Here\'s some sample code to get yourself started:

import java.util.*;

// An interface to be implemented by everyone interested in \"Hello\" events
interface HelloListener {
    void someoneSaidHello();
}

// Someone who says \"Hello\"
class Initiater {
    private List<HelloListener> listeners = new ArrayList<HelloListener>();

    public void addListener(HelloListener toAdd) {
        listeners.add(toAdd);
    }

    public void sayHello() {
        System.out.println(\"Hello!!\");

        // Notify everybody that may be interested.
        for (HelloListener hl : listeners)
            hl.someoneSaidHello();
    }
}

// Someone interested in \"Hello\" events
class Responder implements HelloListener {
    @Override
    public void someoneSaidHello() {
        System.out.println(\"Hello there...\");
    }
}

class Test {
    public static void main(String[] args) {
        Initiater initiater = new Initiater();
        Responder responder = new Responder();

        initiater.addListener(responder);

        initiater.sayHello();  // Prints \"Hello!!!\" and \"Hello there...\"
    }
}

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Related article: Java: Creating a custom event

回答2:

What you want is an implementation of the observer pattern. You can do it yourself completely, or use java classes like java.util.Observer and java.util.Observable

回答3:

There are 3 different ways you may wish to set this up:

1. Thrower inside of Catcher
2. Catcher inside of Thrower
3. Thrower and Catcher inside of another class in this example Test

THE WORKING GITHUB EXAMPLE I AM CITING Defaults to Option 3, to try the others simply uncomment the \"Optional\" code block of the class you want to be main, and set that class as the ${Main-Class} variable in the build.xml file:

4 Things needed on throwing side code:

import java.util.*;//import of java.util.event

//Declaration of the event\'s interface type, OR import of the interface,
//OR declared somewhere else in the package
interface ThrowListener {
    public void Catch();
}
/*_____________________________________________________________*/class Thrower {
//list of catchers & corresponding function to add/remove them in the list
    List<ThrowListener> listeners = new ArrayList<ThrowListener>();
    public void addThrowListener(ThrowListener toAdd){ listeners.add(toAdd); }
    //Set of functions that Throw Events.
        public void Throw(){ for (ThrowListener hl : listeners) hl.Catch();
            System.out.println(\"Something thrown\");
        }
////Optional: 2 things to send events to a class that is a member of the current class
. . . go to github link to see this code . . .
}

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2 Things needed in a class file to receive events from a class

/*_______________________________________________________________*/class Catcher
implements ThrowListener {//implement added to class
//Set of @Override functions that Catch Events
    @Override public void Catch() {
        System.out.println(\"I caught something!!\");
    }
////Optional: 2 things to receive events from a class that is a member of the current class
. . . go to github link to see this code . . .
}