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Java

Tracy Bowers
Tracy Bowers
10,136 Points
Posted by Tracy Bowers
Tracy Bowers
10,136 Points

Event handler explanation. Too advanced to fast?

Craig/all, jumping to passing Lambdas to the even handler lost me. Perhaps I would have benefited in learning the old way first. Event handlers and life before Lambdas. After all Lambdas are relatively new to Java,

How would one use an event handler without a Lambda? Lambdas are relatively new to Java I think. How did our forefathers implement event handlers. :-)

1 Answer

Mihai Craciun
Mihai Craciun
13,520 Points

Let's take a simple example, adding an event handler to a button:

This is how it should look like without lambda

playButton.setOnAction(new EventHandler<ActionEvent>(){
    @Override
    public void handle(ActionEvent event) {
        System.out.println("Playing!");
    }
});

And this is how it should look like with lambda

playButton.setOnAction(event -> System.out.println("Playing!"));

As you can see lambdas are much more concise and not that hard to understand as long as you know what to point

Tracy Bowers
Tracy Bowers
10,136 Points
Tracy Bowers
Tracy Bowers
10,136 Points

Thanks for the response. Wrapping my head around passing whole functions as parameters. Brain just went POOF!

What I think is happening here is this: The event handler needs to do something when the event is triggered. That something needs to be packaged into a function and a reference to that function needs to be registered with the event handler.

Agreed that the Lambda was a good thing; however, what if your function needs to be more complex? Does it make sense jamming it all in as a parameter? Can the function exist as a regular function and that regular function be passed as a parameter?

Mihai Craciun
Mihai Craciun
13,520 Points

Well if the function is more complex you only need to add parentheses like this

playButton.setOnAction(event -> {
System.out.println("Playing!"));
System.out.println("Still Playing");
});

but if you really want to pass it as a parameter nobody stops you

public void saySth(String something) {
    System.out.println(something);
    //code code code
}

//some other code

playButton.setOnAction(event -> saySth("Paying!"));