Free Data Structures and Algorithms Course









Subscribe below and get all best seller courses for free !!!










OR



Subscribe to all free courses

What do we mean by Annotations in Java programming language ?.

What are Annotations in Java ?.

Annotations in Java are metadatas that adds information to your code in a formal way so that you can keep track to the information added at a later stage. They provide a Java programmer information which describes the program fully in a sophisticated way. Annotations help us in generating descriptor files and giving us way to write boilerplate code each time.

Annonations in Java have a symbol @ in its syntax declaration. Java contains general purpose built in annotations defined in java.lang package as :

1. @Override : This annotation is used over method which we intend to override in sub-class. It generates compile-time error if we accidentally give method signature incorrect at the time of overriding.

2. @Deprecated : Generally, it gives a programmer a compiler warning if he wishes to use a thing which is marked as Deprecated.

3. @SuppressWarnings : Generally, it is used when we want compiler to turn off the warnings it is displaying.

There are meta-annotations in Java programming language too that provides information while creating an annotation. Some of the meta-annotation are as follows :

1. @Target : This meta-annotation gives information about a annotation that where it is supposed to be applied. It has property as ElementType. The values it takes is of form :

i.   CONSTRUCTOR : For Constructor declarations.
ii.  FIELD : For Field declarations.
iii. LOCAL_VARIABLE : For local variable declarations.
iv.  TYPE : For class , interface , enum declarations.
v.   PARAMETER : For parameter declarations.
vi.  PACKAGE : For the package declarations.
vii. METHOD : For the method declarations.

2. @Retention : This meta-annotation gives general limit as how long the information in annotation should be kept. It has property as RetentionPolicy. The values it takes is of form :

i.   SOURCE : The annotation usage is at source level and generally discarded by the compiler.
ii.  CLASS : The annotation usage is at class file level, used by the compiler and generally discarded by the VM.
iii. RUNTIME : The annotation usage is at runtime level, used by the VM to be read reflectively.

3. @Documented : This meta-annotation is mostly used in the javadocs.

4. @Inherited : This meta-annotation allows all the sub-classes to inherit parent annotations.
 
© 2021 Learn Java by Examples Template by Hubberspot