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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Daemon thread is a low priority thread. It runs intermittently in the back ground, and takes care of the garbage collection operation for the java runtime system. By calling setDaemon() method is used to create a daemon thread.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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