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How to assign default values to custom annotations?


Description:

  • We can assign default values to annotation members. These values will be return incase if you didn't provide any values to the annotation members.
  • We can assign default values by using default clause during members declarations. Make sure that the default values are same type as members.
  • Below example shows how to assign default vlaues to annotation members.


Code:
package com.java2novice.annotations;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Method;


@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnot{
	
	String key() default "site";
	String value() default "java2novice.com";
}

public class MyAnnotDefaultValues {

	@MyAnnot()
	public void myAnnotationTestMethod(){
		
		try {
			Class<? extends MyAnnotDefaultValues> cls = this.getClass();
			Method mth = cls.getMethod("myAnnotationTestMethod");
			MyAnnot myAnno = mth.getAnnotation(MyAnnot.class);
			System.out.println("key: "+myAnno.key());
			System.out.println("value: "+myAnno.value());
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	public static void main(String a[]){
		
		MyAnnotDefaultValues mat = new MyAnnotDefaultValues();
		mat.myAnnotationTestMethod();
	}
}

Output:
key: site
value: java2novice.com
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Accessing elements are faster with ArrayList, because it is index based. But accessing is difficult with LinkedList. It is slow access. This is to access any element, you need to navigate through the elements one by one. But insertion and deletion is much faster with LinkedList, because if you know the node, just change the pointers before or after nodes. Insertion and deletion is slow with ArrayList, this is because, during these operations ArrayList need to adjust the indexes according to deletion or insetion if you are performing on middle indexes. Means, an ArrayList having 10 elements, if you are inserting at index 5, then you need to shift the indexes above 5 to one more.
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
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