07-Java8新特性 其他新特性

重复注解与类型注解

Java8对注解处理提供了两点该进,可重复的注解及https://www.fons.https://www.fons.com.cn/tag/co" target="_blank">com.cn/tag/%e5%8f%af%e7%94%a8" target="_blank">可用于类型的注解

重复注解定义使用

新建注解

package com.dance.java8.day01.annotati++on;
i++mport java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.ElementType.LOCAL_VARIABLE;
// 重复注解 必须使用@Repeatable修饰 并指定注解容器
@Repeatable(MyAnnotations.class)
@Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
String value() default "flower";
}

新建注解容器

package com.dance.java8.day01.annotation;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.*;
@Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotations {
MyAnnotation[] value();
}

新建测javascript百炼成仙试类

package com.dance.java8.day01.annotation;
import java.lang.reflect.Method;
import java.util.Arrays;
/**
* 重复注解与类型注解
*/
public class TestAnnotation {
public static void main(String[] args) throws NoSuchMethodException {
Class<TestAnnotation> testAnnotationClass = TestAnnotation.class;
Method show = testAnnotationClass.getMethod("show");
Arrays.stream(show.getAnnotationsByType(MyAnnotation.class)).forEach(System.out::println);
}
@MyAnnotation("flower")
@MyAnnotation("dance")
public void show(){
}
}

执行结果

@com.dance.java8.day01.annotation.MyAnnotation(value=flower)
@com.dance.java8.day01.annotation.MyAnnotation(value=dance)

类型注解定义使用

修改注解,增加类型注解

package com.dance.java8.day01.annotation;
import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.ElementType.LOCAL_VARIABLE;
// 重复注解 必须使用@Repeatable修饰 并指定注解容器
@Repeatable(MyAnnotations.class)
@Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE, TYPE_PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
String value() default "flower";
}

修改测试类

package com.dance.java8.day01.annotation;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.util.Arrays;
/**
* 重复注解与类型注解
*/
public class TestAnnotation {
public static void main(String[] args) throws NoSuchMethodException {
Class<TestAnnotation> testAnnotationClass = TestAnnotation.class;
Method show = testAnnotationClass.getMethod("show",String.class);
Arrays.stream(show.getAnnotationsByType(MyAnnotation.class)).forEach(System.out::println);
Annotation[][] parameterAnnotations = show.getParameterAnnotations();
Arrays.stream(parameterAnnotations).forEach(x-> Arrays.stream(x).forEach(System.out::println));
}
@MyAnnotation("flower")
@MyAnnotation("dance")
public void show(@MyAnnotation("string") String s){
}
}

执行结果

@com.dance.java8.day01.annotation.MyAnnotation(value=flower)
@com.dance.java8.day01.annotation.MyAnnotation(value=dance)
@com.dance.java8.day01.annotation.MyAnnotation(value=string)

作者:彼岸舞