Java Function as Parameter

Question

I am trying to add key press events to my library, so is it possible to pass a function as a parameter to one of my library's classes, then when my library needs to fire off that function?

example:

Library lib = new Library();
lib.myAction(function(){
    // Do some java stuff here
});

So with that, when my library see something take place, such as a key press, it will fire off that function. If you have every worked with JavaScript you can do this (Really common with jQuery), and I would like to have the same effect but with Java.

perhaps you could create an enum that represent each function() then pass that? — bonCodigo
– bonCodigo, Commented Dec 23, 2012 at 20:52
The way you can handle it in Java now (without lambda's in JDK8) is to implement Command or Strategy design pattern — Xeon
– Xeon, Commented Dec 23, 2012 at 20:58

Jon Skeet · Accepted Answer · 2012-12-23 20:52:17Z

7

No, there's no direct equivalent of that in Java. The closest you can get is to have an interface or abstract class, and then use anonymous inner class to implement/extend it:

lib.myAction(new Runnable() {
    @Override public void run() {
        // Do something here
    }
});

This should be made much simpler by Java 8's lambda expression support.

answered Dec 23, 2012 at 20:52

Jon Skeet

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1 Comment

MrSmith42 Over a year ago

We all hope for such features in the next java version, whenever it will come.

ovunccetin · Accepted Answer · 2012-12-23 21:36:58Z

0

There is no simple way for this in Java. However you can pass a Method object (the method must be static) to your myAction function and invoke the passed method in it as follows:

public Object myAction(Method m, Object... args) {
    return m.invoke(args);
}

Note that the args parameter is the parameter list of the passed method.

For example, suppose you have a class A and a static method sampleMethod(String s) defined in A. You can call your myAction method as follows:

lib.myAction(A.class.getMethod("sampleMethod", String.class), "Value of parameter s");

If your sampleMethod is parameterless then you can omit the second parameter:

lib.myAction(A.class.getMethod("sampleMethod", String.class));

answered Dec 23, 2012 at 21:36

ovunccetin

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