Annotation: Annotation. New technologies introduced by JDK5.0
The role of annotations:
①Not the program itself, you can explain the program
②Can be read by other programs
Annotation format: @Annotation name. In addition, you can add some parameter values
//例
@SuppressWarnings(value="unchecked")Where can annotations be used?
It can be attached to package, class, method, filed, etc., which is equivalent to adding additional auxiliary information to them, and can programmatically access these metadata through reflection mechanism
Built-in annotations:
| @Override | Defined in java.lang.Override, it is used to decorate methods, indicating that a method declaration intends to override another method declaration of the superclass |
| @Deprecated | Decorate a method, property, class to indicate that programmers are discouraged from using such an element, usually because it is dangerous or a better alternative exists |
| @SuppressWarnings | Used to suppress compile-time warning messages, you need to add a parameter to use |
@Override
@Deprecated
@SuppressWarnings
If you define an element that is not used, a Variable is never used warning will appear
Add @SuppressWarnings("all") before the method to suppress the warning message
@SuppressWarnings can also be added in front of the class
Meta- annotation : meta-annotation type, responsible for annotating other annotations, used to describe other annotation types
| @Target | Used to describe the scope of use of the annotation |
| @Retention | Declaration cycle used to describe annotations SOURCE<CLASS<RUNTIME |
| @Document | Indicates that the annotation is included in the javadoc |
| @Inherited | Indicates that subclasses can inherit the annotation from the parent class |
Define a meta-annotation:
@Target: Indicates where the annotation can be used
@Retention: Define the period of the annotation, generally set to RUNTIME to indicate that it is valid at runtime
@Document indicates whether to generate annotations in JAVAdoc
@Inherited subclasses can inherit the annotations of the parent class
Custom annotations:
@interface custom annotation, which automatically inherits the java.lang.annotation.Annotation interface
Parameters with default values:
