What is a java marker interface?
Java Marker Interface Examples:
java.lang.Cloneable
java.io.Serializable
java.util.EventListener
Lets take the java.io.Serializable marker interface. It doesnot has any members defined it it. When a java class is to be serialized, you should intimate the java compiler in some way that there is a possibility of serializing this java class. In this scenario, marker interfaces are used. The java class which may be serialized has to implement the java.io.Serializable marker interface. In such way, we are intimating the java compiler.
From java 1.5, the need for marker interface is eliminated by the introduction of the java annotation feature. So, it is wise to use java annotations than the marker interface. It has more feature and advantages than the java marker interface.
Difference Between Interface and Abstract Class
- Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behavior.
- Variables declared in a Java interface is by default final. An abstract class may contain non-final variables.
- Members of a Java interface are public by default. A Java abstract class can have the usual flavors of class members like private, protected, etc..
- Java interface should be implemented using keyword “implements”; A Java abstract class should be extended using keyword “extends”.
- An interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces.
- A Java class can implement multiple interfaces but it can extend only one abstract class.
- Interface is absolutely abstract and cannot be instantiated; A Java abstract class also cannot be instantiated, but can be invoked if a main() exists.
- In comparison with java abstract classes, java interfaces are slow as it requires extra indirection.
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