what is a marker interface in java
A marker interface in Java is an interface with no methods or fields; it acts as a tag to inform the compiler that the classes implementing it should be treated differently. Marker interfaces are also known as tag interfaces. They simply mark or tag a class to indicate that it possesses a certain property or behavior.
One common use case for marker interfaces is in frameworks or APIs where the presence of a marker interface implies some sort of contract or special handling.
Here’s an example of a marker interface in Java:
In this example,
Printable is a marker interface with no methods. The
Document class implements the
Printable interface, indicating that it can be printed. The
Image class does not implement the
PrintProcessor class has a
Object as a parameter. It checks if the object is an instance of the
Printable interface. If it is, the object is considered printable, and the logic to print the object can be executed. Otherwise, a message indicating that the object cannot be printed is displayed.
Marker interfaces are used sparingly in modern Java development, as annotations and other techniques have largely replaced them. However, they provide a clear and simple way to convey metadata about classes.