javolution.lang.Constant Maven / Gradle / Ivy
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/*
* Javolution - Java(TM) Solution for Real-Time and Embedded Systems
* Copyright (C) 2012 - Javolution (http://javolution.org/)
* All rights reserved.
*
* Permission to use, copy, modify, and distribute this software is
* freely granted, provided that this notice is preserved.
*/
package javolution.lang;
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;
/**
* Indicates that the state of a class instance, a static field or a
* method return value / parameter will not change ever. For parameters
* tagged {@code Constant}, defensive copy is unnecessary.
* [code]
* @Constant(comment="Immutable")
* class Polygon extends Shape {
* private Point2D[] vertices;
* public Polygon(@Constant Point2D... vertices) {
* this.vertices = vertices; // No defensive copying required.
* }
* @Constant(comment="Unmodifiable View")
* List getVertices() {
* return ConstantTable.of(vertices); // Unmodifiable array wrapper.
* }
* }[/code]
*
* The constant annotation is primarily for API documentation purpose but
* static analyzers could also be used to detect constant rules violations.
* [code]
* Polygon triangle = new Polygon(p1, p2, p3); // Ok, literals are always constant.
* Point2D[] vertices = new Point2D[] { p1, p2, p3 };
* triangle = new Polygon(vertices); // vertices is now assumed constant.
* vertices[0] = null; // Rule violation, modification after vertices has been assumed constant!
* [/code]
*
* @author Jean-Marie Dautelle
* @version 6.1, February 2, 2014
*/
@Documented
@Inherited
@Target({ ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER,
ElementType.LOCAL_VARIABLE})
@Retention(RetentionPolicy.CLASS)
public @interface Constant {
/**
* Indicates if this element is constant (default {@code true}).
*/
boolean value() default true;
/**
* Provides additional information (default {@code ""}).
*/
String comment() default "";
}