package org.testng.annotations;

import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Specifies that the current parameter is optional. TestNG will pass in a specified default value,
 * or <code>null</code> if none is specified.
 */
@Retention(RUNTIME)
@Target({PARAMETER})
public @interface Optional {
  /**
   * The default value to pass to this parameter.
   *
   * <p>The default deserves a bit of explanation. JSR-175 (which defines annotations) says that
   * Java annotation parameters can only be ConstantExpressions, which can be primitive/string
   * literals, but not <code>null</code>.
   *
   * <p>In this case, we use this string as a substitute for <code>null</code>; in practice, TestNG
   * will pass <code>null</code> to your code, and not the string "null", if you do not specify a
   * default value here in this parameter.
   *
   * @return the value (default NULL_VALUE)
   */
  String value() default Parameters.NULL_VALUE;
}
