如果存在註釋,java.lang.reflect.Constructor.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.Constructor.getAnnotation(Class <T> annotationClass)
方法的宣告。
public <T extends Annotation> T getAnnotation(Class<T> annotationClass)
引數
Class
物件。返回值
如果存在於此元素,返回該元素的注釋指定的注釋型別,否則返回:null
。
例外
NullPointerException
- 如果給定的注釋類為空。以下範例顯示了java.lang.reflect.Constructor.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.Constructor;
public class ConstructorDemo {
public static void main(String[] args) {
Constructor[] constructors = SampleClass.class.getConstructors();
Annotation annotation = constructors[0].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 {
private String sampleField;
@CustomAnnotation(name="sampleClassConstructor", value = "Sample Constructor Annotation")
public SampleClass(){
}
public SampleClass(String sampleField){
this.sampleField = 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: sampleClassConstructor
value: Sample Constructor Annotation