package org.junit;

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

Annotates fields that reference rules or methods that return a rule. A field must be public, not static, and a subtype of TestRule (preferred) or MethodRule. A method must be public, not static, and must return a subtype of TestRule (preferred) or MethodRule. 
 The Statement passed to the TestRule will run any Before methods, then the Test method, and finally any After methods, throwing an exception if any of these fail. If there are multiple annotated Rules on a class, they will be applied in order of methods first, then fields. However, if there are multiple fields (or methods) they will be applied in an order that depends on your JVM's implementation of the reflection API, which is undefined, in general. Rules defined by fields will always be applied after Rules defined by methods, i.e. the Statements returned by the former will be executed around those returned by the latter. 
Usage

For example, here is a test class that creates a temporary folder before
each test method, and deletes it after each:
public static class HasTempFolder {
    @Rule
    public TemporaryFolder folder= new TemporaryFolder();
    @Test
    public void testUsingTempFolder() throws IOException {
        File createdFile= folder.newFile("myfile.txt");
        File createdFolder= folder.newFolder("subfolder");
        // ...
    }
}


And the same using a method.
public static class HasTempFolder {
    private TemporaryFolder folder= new TemporaryFolder();
    @Rule
    public TemporaryFolder getFolder() {
        return folder;
    }
    @Test
    public void testUsingTempFolder() throws IOException {
        File createdFile= folder.newFile("myfile.txt");
        File createdFolder= folder.newFolder("subfolder");
        // ...
    }
}

 For more information and more examples, see TestRule. 
Ordering
 You can use order() if you want to have control over the order in which the Rules are applied. 
public class ThreeRules {
    @Rule(order = 0)
    public LoggingRule outer = new LoggingRule("outer rule");
    @Rule(order = 1)
    public LoggingRule middle = new LoggingRule("middle rule");
    @Rule(order = 2)
    public LoggingRule inner = new LoggingRule("inner rule");
    // ...
}

Since:
4.7/**
 * Annotates fields that reference rules or methods that return a rule. A field must be public, not
 * static, and a subtype of {@link org.junit.rules.TestRule} (preferred) or
 * {@link org.junit.rules.MethodRule}. A method must be public, not static,
 * and must return a subtype of {@link org.junit.rules.TestRule} (preferred) or
 * {@link org.junit.rules.MethodRule}.
 * <p>
 * The {@link org.junit.runners.model.Statement} passed
 * to the {@link org.junit.rules.TestRule} will run any {@link Before} methods,
 * then the {@link Test} method, and finally any {@link After} methods,
 * throwing an exception if any of these fail.  If there are multiple
 * annotated {@link Rule}s on a class, they will be applied in order of methods first, then fields.
 * However, if there are multiple fields (or methods) they will be applied in an order
 * that depends on your JVM's implementation of the reflection API, which is
 * undefined, in general. Rules defined by fields will always be applied
 * after Rules defined by methods, i.e. the Statements returned by the former will
 * be executed around those returned by the latter.
 *
 * <h3>Usage</h3>
 * <p>
 * For example, here is a test class that creates a temporary folder before
 * each test method, and deletes it after each:
 * <pre>
 * public static class HasTempFolder {
 *     &#064;Rule
 *     public TemporaryFolder folder= new TemporaryFolder();
 *
 *     &#064;Test
 *     public void testUsingTempFolder() throws IOException {
 *         File createdFile= folder.newFile(&quot;myfile.txt&quot;);
 *         File createdFolder= folder.newFolder(&quot;subfolder&quot;);
 *         // ...
 *     }
 * }
 * </pre>
 * <p>
 * And the same using a method.
 * <pre>
 * public static class HasTempFolder {
 *     private TemporaryFolder folder= new TemporaryFolder();
 *
 *     &#064;Rule
 *     public TemporaryFolder getFolder() {
 *         return folder;
 *     }
 *
 *     &#064;Test
 *     public void testUsingTempFolder() throws IOException {
 *         File createdFile= folder.newFile(&quot;myfile.txt&quot;);
 *         File createdFolder= folder.newFolder(&quot;subfolder&quot;);
 *         // ...
 *     }
 * }
 * </pre>
 * <p>
 * For more information and more examples, see
 * {@link org.junit.rules.TestRule}.
 *
 * <h3>Ordering</h3>
 * <p>
 * You can use {@link #order()} if you want to have control over the order in
 * which the Rules are applied.
 *
 * <pre>
 * public class ThreeRules {
 *     &#064;Rule(order = 0)
 *     public LoggingRule outer = new LoggingRule("outer rule");
 *
 *     &#064;Rule(order = 1)
 *     public LoggingRule middle = new LoggingRule("middle rule");
 *
 *     &#064;Rule(order = 2)
 *     public LoggingRule inner = new LoggingRule("inner rule");
 *
 *     // ...
 * }
 * </pre>
 *
 * @since 4.7
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
public @interface Rule {

    int DEFAULT_ORDER = -1;

    
Specifies the order in which rules are applied. The rules with a higher value are inner.
Since:
4.13/**
     * Specifies the order in which rules are applied. The rules with a higher value are inner.
     *
     * @since 4.13
     */
    int order() default DEFAULT_ORDER;

}