OCP Chapter 13

Annotations

assign metadata tp classes methods variables and other Java types
an annotation ascribes custom information on the declaration where it is defined
annotations zal compileren niet in de weg zitten
case sensitive!
zijn impliciet abstract =. dus geen protected, private en final
required element, optional element, constant element
all requiremed elements must be provided
marker annotation has no elements

// creeerr Annotatie
public @interface Exercise {}

// gebruik m
@Exercise public class Blah{}

annotation element

zonder value => dan dus REQUIRED

public @interface Exercise {
 int hoursPerDay();
}

// =>

@Exercise(hoursPerDay=34)public class Blah {}

providing an optional element with default

NOT NULL
type mag primitive, Class, enum, another annotation or an array of these types
leeg mag wel => "" als empty String

public @interface Exercise {
 int hoursPerDay();
 int startHour() default 6; // optional element
}

Adding a constant var

public @interface Exercise {
 int MINVALUE = 21;
}

Applying Annotations

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