JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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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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Prevent a method from being overridden
By specifying final keyword to the method you can avoid overriding in a subcalss. Similarlly one can use final at class level to prevent creating subclasses.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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