Annotations

• Java Annotations are used to add metadata information into our code
• Annotations doesn't affect the execution of the program

Built-in Annotations in Java

Java has three built-in Annotations. They are :

• @Override
• @Deprecated
• @SupressWarnings

1. @Override

• We should use this annotation while overriding the child class method

Example

class A {
  public void show () {
    System.out.println("Class A");
  }
}

class B extends A {
  
  @Override
  public void show () {
    System.out.println("Class B");
  }
  public static void main (String[] args) {
    B ob = new B();
    ob.show();
  }
}

check output here

2. @Deprecated

• Used to mark elements that are no longer used
• Compiler gives a warning when Deprecated elements are used

Example

class Example {
  void read2 () {
    System.out.println("updated method");
  }
  
  @Deprecated
  void read1 () {
    System.out.println("outdated method");
  }
}

class Main {
    public static void main(String[] args) {
        Example ob = new Example();
        ob.read2();
        ob.read1();
    }
}

check output here

3. @SupressWarnings

• Used to tell the compiler, to ignore specific warnings

Example

class Example { 
	@Deprecated
	public void show() { 
		System.out.println("outdated function"); 
	} 
} 

class Main { 
	@SuppressWarnings({"checked", "deprecation"}) 
	public static void main(String args[]) { 
		Example ob = new Example(); 
		ob.show(); 
	} 
} 

Built-in Java Annotations used in other annotations

1. @Target

Used to specify at which type, the annotation should be used

2. @Retention

Used to specify the level at which the annotation is available

3. @Inherited

Marks the annotation should be inherited to the subclasses

4. @Documented

Used to tell an element should be Documented by JavaDoc