what's difference between a callback and observer pattern in java

Question

I was going through the following link in stack over flow

How do I perform a JAVA callback between classes?

In the particular question answer 18 refers to callbacks and answer 9 refers to the observer pattern.

I am unable to distinguish the difference between both.

Can anyone please explain where these two approaches differ?

Answer 1

A callback is basically a piece of code that your provide for a class and gets called by it at a certain point. Ex:

serverConnectionHandler = new ServerConnections(new ITypedCallback<Socket>() {
        @Override
        public void execute(Socket socket) {
            // do something with your socket here
        }
});

The observer's pattern is a design pattern that is based on callbacks. You can find more details about it here http://en.wikipedia.org/wiki/Observer_pattern.