An interface is an entity through which unrelated objects interact with each other. An interface could also resemble the rules of a communication protocol or an adherence of two sides to a business agreement (one side agrees to do a service while the other side promises to pay money). Similarly, a class that implements an interface agrees to implement all of the
methods defined in the interface (agrees to a certain
behavior).
However, a Java interface can declare methods but cannot implement them, because method bodies are missing: // Declare an interface -- methods declared in the interface are public and abstract Note: An interface is not an object; therefore, it cannot be instantiated. Note: However, interfaces can be extended by other interfaces or implemented by classes. To implement an interface class must use implements keyword: // A class can extend only one superclass, but it can implement multiple interfaces An object can be referenced by multiple data types: by the type of every interface they implement as well as by the type of their class. Therefore, a variable declared as an interface type can reference any object that is instantiated from any class implementing the interface. public static void main(String args[]){ Greeting hello = new Greeting(); hello.displayGreeting(); } |
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