Abstraction in Java is achieved by using interface and abstract class in Java. An interface or abstract class is something which is not concrete , something which is incomplete.
One example of Abstraction is creating interface to denote common behaviour without specifying any details about how that behaviour works e.g. You create an interface called Server which has start() and stop() method. This is called abstraction of Server because every server should have way to start and stop and details may differ.
