Java8对注解处理提供了两点改进：可重复的注解及可用于类型的注解。
一、重复注解
package com.expgiga.Java8;
import 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.
CONSTRUCTOR;
import static java.lang.annotation.ElementType.
LOCAL_VARIABLE;
/**
* 自定义注解
*/
@Repeatable(
MyAnnotations.
class)
@Target({
TYPE,
FIELD,
METHOD,
PARAMETER,
CONSTRUCTOR,
LOCAL_VARIABLE})
@Retention(RetentionPolicy.
RUNTIME)
public @
interface MyAnnotation {
String value()
default "expgiga";
}
package com.expgiga.Java8;
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.
CONSTRUCTOR;
import static java.lang.annotation.ElementType.
LOCAL_VARIABLE;
/**
* 注解容器
*/
@Target({
TYPE,
FIELD,
METHOD,
PARAMETER,
CONSTRUCTOR,
LOCAL_VARIABLE})
@Retention(RetentionPolicy.
RUNTIME)
public @
interface MyAnnotations {
MyAnnotation[] value();
}
package com.expgiga.Java8;
import java.lang.reflect.Method;
/**
* Java8重复注解与类型注解
*/
public class TestAnnotation {
public static void main(String[] args)
throws NoSuchMethodException {
Class<TestAnnotation> clazz = TestAnnotation.
class;
Method m1 = clazz.getMethod(
"show");
MyAnnotation[] mas = m1.getAnnotationsByType(
MyAnnotation.
class);
for (
MyAnnotation myAnnotation : mas) {
System.
out.println(myAnnotation.value());
}
}
@MyAnnotation(
"Hello")
@MyAnnotation(
"World")
public void show() {
}
}
二、类型注解
package com.expgiga.Java8;
import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.ElementType.
CONSTRUCTOR;
import static java.lang.annotation.ElementType.
LOCAL_VARIABLE;
/**
* 自定义注解
*/
@Repeatable(
MyAnnotations.
class)
@Target({
TYPE,
FIELD,
METHOD,
PARAMETER,
CONSTRUCTOR,
LOCAL_VARIABLE,
TYPE_PARAMETER})
@Retention(RetentionPolicy.
RUNTIME)
public @
interface MyAnnotation {
String value()
default "expgiga";
}
package com.expgiga.Java8;
import java.lang.reflect.Method;
/**
* Java8重复注解与类型注解
*/
public class TestAnnotation {
//checker framework
private /*@NotNull*/ Object
obj =
null;
public static void main(String[] args)
throws NoSuchMethodException {
Class<TestAnnotation> clazz = TestAnnotation.
class;
Method m1 = clazz.getMethod(
"show");
MyAnnotation[] mas = m1.getAnnotationsByType(
MyAnnotation.
class);
for (
MyAnnotation myAnnotation : mas) {
System.
out.println(myAnnotation.value());
}
}
@MyAnnotation(
"Hello")
@MyAnnotation(
"World")
public void show(
@MyAnnotation(
"abc") String str) {
}
}
