如果存在這樣的註釋,則java.lang.reflect.Field.getAnnotation(Class <T> annotationClass)
方法返回指定型別的元素的注釋,否則返回為null
。
以下是java.lang.reflect.Field.getAnnotation(Class <T> annotationClass)
方法的宣告。
public <T extends Annotation> T getAnnotation(Class<T> annotationClass)
引數
null
。返回值
null
。異常
null
,該欄位為範例欄位。以下範例顯示java.lang.reflect.Field.getAnnotation(Class<T> annotationClass)
方法的用法。
import java.lang.annotation.Annotation;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Field;
public class GetAnnotation {
public static void main(String[] args) throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
Field field = SampleClass.class.getField("sampleField");
Annotation annotation = field.getAnnotation(CustomAnnotation.class);
if(annotation instanceof CustomAnnotation){
CustomAnnotation customAnnotation = (CustomAnnotation) annotation;
System.out.println("name: " + customAnnotation.name());
System.out.println("value: " + customAnnotation.value());
}
}
}
@CustomAnnotation(name="SampleClass", value = "Sample Class Annotation")
class SampleClass {
@CustomAnnotation(name="sampleClassField", value = "Sample Field Annotation")
public String sampleField;
public String getSampleField() {
return sampleField;
}
public void setSampleField(String sampleField) {
this.sampleField = sampleField;
}
}
@Retention(RetentionPolicy.RUNTIME)
@interface CustomAnnotation {
public String name();
public String value();
}
讓我們編譯並執行上面的程式,這將產生以下結果 -
name: sampleClassField
value: Sample Field Annotation