注解和反射笔记
自定义两个注解
@Target({ElementType.CONSTRUCTOR, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)//运行时加载Annotation 到JVM 中，只有此状态可通过反射获取注解的信息。
@interface A {String value() default "默认构造方法";//成员
}
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@interface B {String describe();Class<?> type() default void.class;
}
把以上两个注解来注解一个类
@A
public class Record {@B(describe="编号", type=int.class)int id;@B(describe="姓名", type=String.class)String name;@A()public Record() {}@A("立即初始化构造函数")public Record(@B(describe="编号", type=int.class) int id,@B(describe="姓名", type=String.class) String name) {this.id = id;this.name = name;}@B(describe="获取id", type=int.class)public int getId() {return id;}@B(describe="设置id", type=int.class)public void setId(@B(describe="编号", type=int.class) int id) {this.id = id;}@B(describe="获取姓名", type=String.class)public String getName() {return name;}@B(describe="设置姓名", type=String.class)public void setName(@B(describe="姓名", type=String.class) String name) {this.name = name;}
}
测试类
public class TestAnnotation {
public static void main(String[] args) throws Exception {Class<?> clazz = Record.class;System.out.println("类上是否有注解：" + clazz.isAnnotationPresent(A.class));A a = clazz.getAnnotation(A.class);System.out.println("A注解的value值：" + a.value());System.out.println("---------");System.out.println("属性上的注解：");Field[] fields = clazz.getDeclaredFields();for(Field f: fields) {System.out.println(f.getName() + ": ");Annotation[] annotations = f.getAnnotations();//与注解本身名字有何不同呢？其实就是多态for(Annotation annotation: annotations) {System.out.println(" " + annotation);}}System.out.println("---------");System.out.println("构造方法上的注解：");Constructor<?>[] constructors = clazz.getDeclaredConstructors();for (Constructor<?> constructor : constructors) {constructor.setAccessible(true);System.out.println(constructor);Annotation[] annotations = constructor.getAnnotations();for (Annotation annotation : annotations) {System.out.println(" " + annotation);}}System.out.println("---------");System.out.println("方法上的注解：");Method[] methods = clazz.getDeclaredMethods();for(Method m: methods) {System.out.println(m.getName() + ":");Annotation[] annotations = m.getDeclaredAnnotations();for(Annotation annotation: annotations) {System.out.println(" " + annotation);}}}
}
运行结果
类上是否有注解：true
A注解的value值：默认构造方法
属性上的注解：
id:@com.qhf.annotation.B(type=int, describe=编号)
name:
@com.qhf.annotation.B(type=class java.lang.String, describe=姓名)
构造方法上的注解：
public com.qhf.annotation.Record()@com.qhf.annotation.A(value=默认构造方法)
public com.qhf.annotation.Record(int,java.lang.String)
@com.qhf.annotation.A(value=立即初始化构造函数)
方法上的注解：
getName:@com.qhf.annotation.B(type=class java.lang.String, describe=获取姓名)
getId:
@com.qhf.annotation.B(type=int, describe=获取id)
setName:
@com.qhf.annotation.B(type=class java.lang.String, describe=设置姓名)
setId:
@com.qhf.annotation.B(type=int, describe=设置id)
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