What does "Code as Data" mean?

Question

I recently came across a presentation from EclipseCon 2014, where on page 5 they say "Lambda expressions allow you to treat code as data".

I also came across this example code

button.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent event) {
        System.out.println("button clicked");
    }
});

from "Java 8 Lambdas: Pragmatic Functional Programming" by Richard Warburton where he says

"This is actually an example of using code as data—we’re giving the button an object that represents an action."

What does code as data mean with respect to Lambda expressions and/or anonymous inner class?

Answer 1

As you pass functionality as an argument to another method, such as what action should be taken when someone clicks a button like your example code.

Lambda expressions enable you to do this, to treat functionality as method argument = code as data.

See oracle linkfor more info and lambda code examples.