GeezerVison

Built-in annotations

public class Animal {
    public void speak() {}

    public String getType() {
        return "Generic animal";
    }
}

public class Cat extends Animal {
    @Override
    public void speak() { // This is a good override.
        System.out.println("Meow.");
    }

    @Override
    public String gettype() { // Compile-time error due to typo: should be getType() not gettype().
        return "Cat";
    }
}

Custom annotations

// @Twizzle is an annotation to method toggle().
@Twizzle
public void toggle() {

}

// Declares the annotation Twizzle.
public @interface Twizzle {

}

// Same as: @Edible(value = true)
@Edible(true)
Item item = new Carrot();

public @interface Edible {
    boolean value() default false;
}

@Author(first = "Oompah", last = "Loompah")
Book book = new Book();

public @interface Author {
    String first();
    String last();
}

import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME) // Make this annotation accessible at runtime via reflection.
@Target({ElementType.METHOD}) // This annotation can only be applied to class methods.
public @interface Tweezable {}

package org.wikipedia.examples;

import java.io.Serializable;

import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.GenerationType;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.Table;

@Entity // Declares this an entity bean
@Table(name = "people") // Maps the bean to SQL table "people"
public class Person implements Serializable {
    @Id // Map this to the primary key column.
    @GeneratedValue(strategy = GenerationType.AUTO) // Database will generate new primary keys, not us.
    private Integer id;

    @Column(length = 32) // Truncate column values to 32 characters.
    private String name;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

package org.wikipedia.examples.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({
    ElementType.TYPE, ElementType.METHOD,
    ElementType.CONSTRUCTOR, ElementType.ANNOTATION_TYPE,
    ElementType.PACKAGE, ElementType.FIELD, ElementType.LOCAL_VARIABLE
})
@Inherited
public @interface Unfinished {
    public enum Priority { LOW, MEDIUM, HIGH }
    String value();
    String[] changedBy() default "";
    String[] lastChangedBy() default "";
    Priority priority() default Priority.MEDIUM;
    String createdBy() default "James Gosling";
    String lastChanged() default "2011-07-08";
}

package org.wikipedia.examples.annotation;

public @interface UnderConstruction {
    String owner() default "Patrick Naughton";
    String value() default "Object is Under Construction.";
    String createdBy() default "Mike Sheridan";
    String lastChanged() default "2011-07-08";
}

package org.wikipedia.examples.validators;

import jakarta.faces.application.FacesMessage;
import jakarta.faces.component.UIComponent;
import jakarta.faces.context.FacesContext;
import jakarta.faces.validator.Validator;
import jakarta.faces.validator.ValidatorException;

import org.wikipedia.examples.annotation.UnderConstruction;
import org.wikipedia.examples.annotation.Unfinished;
import org.wikipedia.examples.annotation.Unfinished.Priority;
import org.wikipedia.examples.util.Util;

@UnderConstruction(owner = "Jon Doe")
public class DateValidator implements Validator {
    public void validate(FacesContext context, UIComponent component, Object value) throws ValidatorException {
        String date = (String) value;
        String errorLabel = "Please enter a valid date.";
        if (!component.getAttributes().isEmpty()) {
            errorLabel = (String) component.getAttributes().get("errordisplayval");
        }

        if (!Util.validateAGivenDate(date)) {
            @Unfinished(
                changedBy = "Steve",
                value = "whether to add message to context or not, confirm",
                priority = Priority.HIGH
            )
            FacesMessage message = new FacesMessage();
            message.setSeverity(FacesMessage.SEVERITY_ERROR);
            message.setSummary(errorLabel);
            message.setDetail(errorLabel);
            throw new ValidatorException(message);
        }
    }
}