23. Custom Marker Interface In Java


✔ JAVA CHAPTERS:-

1. Introduction to Java
2. Features of Java
3. Java Virtual Machine
4. D/F B/W JVM, JRE, JDK
5. Java Data Types
6. Java Programs
7. Setting Java Path
8. OOPs Concepts
9. Object & Class In Java
10. OOPs Continued
11. Encapsulation & Polymorphism
12. Method Overloading
13. Method Overriding
14. Dynamic Method Dispatch
15. Association In Java
16. Inheritance in Java
17. Aggregation in java
18. Command Line Argument
19. Execute Command Line
20. Read Input From Command Line
21. Abstract Class In Java
22. Interface in Java
23. Cutom Marker Interface
24. Constructor In Java
25. Package in Java
26. Acess Modifier In Java
27. Static Import In Java
28. Package Class In Java
29. This Keyword
30. Instance Intializer Block
31. Super Keyword
32. Static Keyword
33. Final Keyword



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How To Create Custom Marker Interface In Java

Marker/Tagging Interfaces:

An interface with no methods is known as marker or tagged interface.

Why marker interface used:  

It provides some useful information to JVM/compiler so that JVM/compiler performs some special operations on it. It is used for better readability of code.  Example: Serializable, Clonnable etc. 

Syntax:

public interface Interface_Name {
}

Let us understand it with a example. We have no. of colleges from which some colleges are of A grade. We have created a AGradeCollegeMarker interface which contains no method and only inform the JVM that it is a A grade college. Every A grade college have to implement AGradeCollegeMarker. In TestCollege class, tester method will print “A grade college.” if object belongs to A grade college.

Example:

AGradeCollegeMarker.java
package com.javawithease.business;
 
/**
 * This is marker interface for A grade college.
 * @author java tutorial point
 */
public interface AGradeCollegeMarker {
 
}
College1.java
package com.javawithease.business;
 
/**
 * This class represents a A grade college.
 * @author java tutorial point
 */
public class College1 implements AGradeCollegeMarker{
 //Do something
}
College2.java
package com.javawithease.business;
 
/**
 * This class represents a, non A grade college.
 * @author java tutorial point
 */
public class College2 {
 //Do something
}
TestCollege.java
package com.javawithease.business;
 
/**
 * This class is used to test the custom marker interface functionality.
 * @author java tutorial point
 */
public class TestCollege {
 static void tester(Object obj){
  if (obj instanceof AGradeCollegeMarker) {
                       System.out.println("A grade college.");
                 }
 }
 
 public static void main(String args[]){
  College1 obj1 = new College1();
  College2 obj2 = new College2();
 
  //test college objects
  tester(obj1);
  tester(obj2);
 }
}

Output:

A grade college.

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