Mega Code Archive
0126 Annotation Default Values
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You can give annotation members default values. Those default value are used if no value is specified when the annotation is applied.
A default value is specified by adding a default clause to a member's declaration.
It has this general form:
type member( ) default value;
Here is @MyAnno rewritten to include default values:
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnno {
String str() default "Testing";
int val() default 9000;
}
Either or both can be given values if desired. Therefore, following are the four ways that @MyAnno can be used:
@MyAnno() // both str and val default
@MyAnno(str = "string") // val defaults
@MyAnno(val = 100) // str defaults
@MyAnno(str = "Testing", val = 100) // no defaults
The following program demonstrates the use of default values in an annotation.
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Method;
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnno {
String str() default "Testing";
int val() default 1;
}
public class Main {
@MyAnno()
public static void myMeth() throws Exception{
Main ob = new Main();
Class c = ob.getClass();
Method m = c.getMethod("myMeth");
MyAnno anno = m.getAnnotation(MyAnno.class);
System.out.println(anno.str() + " " + anno.val());
}
public static void main(String args[]) throws Exception{
myMeth();
}
}
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