fine-third/fine-jetbrains/src/org/jetbrains/annotations/Contract.java

/*
 * Copyright 2000-2016 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jetbrains.annotations;

import java.lang.annotation.*;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Specifies some aspects of the method behavior depending on the arguments. Can be used by tools for advanced data flow analysis.
 * Note that this annotation just describes how the code works and doesn't add any functionality by means of code generation.<p>
 *
 * Method contract has the following syntax:<br>
 *  contract ::= (clause ';')* clause<br>
 *  clause ::= args '-&gt;' effect<br>
 *  args ::= ((arg ',')* arg )?<br>
 *  arg ::= value-constraint<br>
 *  value-constraint ::= '_' | 'null' | '!null' | 'false' | 'true'<br>
 *  effect ::= value-constraint | 'fail' <p>
 *
 * The constraints denote the following:<br>
 * <ul>
 * <li> _ - any value
 * <li> null - null value
 * <li> !null - a value statically proved to be not-null
 * <li> true - true boolean value
 * <li> false - false boolean value
 * <li> fail - the method throws an exception, if the arguments satisfy argument constraints
 * </ul>
 * Examples:<p>
 * {@code @Contract("_, null -> null")} - method returns null if its second argument is null<br>
 * {@code @Contract("_, null -> null; _, !null -> !null")} - method returns null if its second argument is null and not-null otherwise<br>
 * {@code @Contract("true -> fail")} - a typical assertFalse method which throws an exception if {@code true} is passed to it<br>
 *
 */
@Documented
@Retention(RetentionPolicy.CLASS)
@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
public @interface Contract {
  /**
   * Contains the contract clauses describing causal relations between call arguments and the returned value
   */
  String value() default "";

  /**
   * Specifies that the annotated method has no visible side effects.
   * If its return value is not used, removing its invocation won't
   * affect program state and change the semantics, unless method call throws an exception.
   * Exception throwing is not considered to be a side effect.
   * <p>
   * Method should not be marked as pure if it does not produce a side-effect by itself,
   * but it could be used to establish a happens-before relation between an event in
   * another thread, so changes performed in another thread might become visible in current thread
   * after this method invocation. Examples of such methods are {@link Object#wait()}, {@link Thread#join()}
   * or {@link AtomicBoolean#get()}. On the other hand, some synchronized methods like {@link java.util.Vector#get(int)}
   * could be marked as pure, because the purpose of synchronization here is to keep the collection internal integrity
   * rather than to wait for an event in another thread.
   * <p>
   * "Invisible" side effects (such as logging) that don't affect the "important" program semantics are allowed.<br><br>
   * <p>
   * This annotation may be used for more precise data flow analysis, and
   * to check that the method's return value is actually used in the call place.
   */
  boolean pure() default false;

  /**
   * Contains a specifier which describes which method parameters can be mutated during the method call.
   * <p>
   *   The following values are possible:
   *   <table summary="">
   *     <tr><td>"this"</td><td>Method mutates the receiver object, and doesn't mutates any objects passed as arguments (cannot be applied for static method or constructor)</td></tr>
   *     <tr><td>"arg"</td><td>Method mutates the sole argument and doesn't mutate the receiver object (if applicable)</td></tr>
   *     <tr><td>"arg1", "arg2", ...</td><td>Method mutates the N-th argument</td></tr>
   *     <tr><td>"this,arg1"</td><td>Method mutates the receiver and first argument and doesn't mutate any other arguments</td></tr>
   *   </table>
   *
   * @return a mutation specifier string
   * Warning: This annotation parameter is experimental and may be changed or removed without further notice!
   */
  String mutates() default "";
}