Callbacks provide a means to register a method to be invoked or called back when an interesting event occurs. Java uses callbacks for applet and servlet life cycle events, AWT and Swing event notifications such as button clicks, and asynchronously reading and writing data from storage and even in Runnable.run() wherein a new thread automatically executes the specified run() method.
In Java, callbacks are typhically typically implemented using interfaces. The general structure of a callback is as follows.
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