java基礎源碼 (4)--reflect包-AnnotatedElement介面

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介面：AnnotatedElement

 * Represents an annotated element of the program currently running in this * VM.  This interface allows annotations to be read reflectively.  All * annotations returned by methods in this interface are immutable and * serializable. The arrays returned by methods of this interface may be modified * by callers without affecting the arrays returned to other callers.　　表示當前在此虛擬機器中啟動並執行程式的注釋元素，該介面允許反射讀取注釋，通過該介面方法返回的所有注釋
都是不可變並且可序列化。通過此介面的方法返回的陳列可以由呼叫著，而不會影響其他調用者返回陣列進行修改。
*/public interface AnnotatedElement {    /**     * Returns true if an annotation for the specified type     * is <em>present</em> on this element, else false.  This method     * is designed primarily for convenient access to marker annotations.　　　　如果此元素上存在指定類型的注釋，則返回true,否則返回false，該方法主要用於方便
　　　　訪問標記注釋
*/    default boolean isAnnotationPresent(Class<? extends Annotation> annotationClass) {        return getAnnotation(annotationClass) != null;    }   /**     * Returns this element‘s annotation for the specified type if     * such an annotation is <em>present</em>, else null.  　　如果這樣的註解存在，就返回該註解，否則返回Null*/    <T extends Annotation> T getAnnotation(Class<T> annotationClass);    /**     * Returns annotations that are <em>present</em> on this element.     *返回此元素上存在的註解 */    Annotation[] getAnnotations();    /**     * Returns annotations that are <em>associated</em> with this element.   返回與此註解相關聯的註解*/    default <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass) {  　　　//預設的調用getDeclaredAnnotationsByte傳入annotationClass作為參數         T[] result = getDeclaredAnnotationsByType(annotationClass);　　　　//如果返回的數組長度大於零，則返回數組，
　　　　//如果返回的數組是零長度而這個AnnotationElement是一個類，
　　　　//並且參數類型是可繼承的註解類型，並且該AnnotatedElement的AnnotatedElement是非空的
　　　　//則返回結果是在父類上調用getAnnotationsByType的結果，具有annotationClass作為論證
　　　　//否則返回零長度的數組
         if (result.length == 0 && // Neither directly nor indirectly present             this instanceof Class && // the element is a class             AnnotationType.getInstance(annotationClass).isInherited()) { // Inheritable             Class<?> superClass = ((Class<?>) this).getSuperclass();             if (superClass != null) {                 // Determine if the annotation is associated with the                 // superclass                 result = superClass.getAnnotationsByType(annotationClass);             }         }         return result;     }    /**     * Returns this element‘s annotation for the specified type if     * such an annotation is <em>directly present</em>, else null.　　　　如果這樣的註解直接存在，則返回指定類型的元素註解，否則返回null，此方法忽略繼承的註解*/    default <T extends Annotation> T getDeclaredAnnotation(Class<T> annotationClass) {         Objects.requireNonNull(annotationClass);         // Loop over all directly-present annotations looking for a matching one         for (Annotation annotation : getDeclaredAnnotations()) {             if (annotationClass.equals(annotation.annotationType())) {                 //更強大，在編譯期間進行動態轉換                 return annotationClass.cast(annotation);             }         }         return null;     }    default <T extends Annotation> T[] getDeclaredAnnotationsByType(Class<T> annotationClass) {        Objects.requireNonNull(annotationClass);        return AnnotationSupport.            getDirectlyAndIndirectlyPresent(Arrays.stream(getDeclaredAnnotations()).                                            collect(Collectors.toMap(Annotation::annotationType,                                                                     Function.identity(),                                                                     ((first,second) -> first),                                                                     LinkedHashMap::new)),                                            annotationClass);    }    /**     * Returns annotations that are <em>directly present</em> on this element.     * This method ignores inherited annotations.  　　　返回直接存在於此元素上的注釋*/    Annotation[] getDeclaredAnnotations();}

 isAnnotationPresent方法的樣本：

@Retention(RetentionPolicy.RUNTIME)@interface Cus{    public String name();    public String value();}@Cus(name = "SampleClass",value = "Sample Class Annotation")class SampClass{    private String sampleFileld;@Cus(name = "sampleMethod",value = "sample Method Annotation")    public String sampleMethod(){        return "sample";    }    public String getSampleFileld(){        return sampleFileld;    }    public void setSampleFileld(String sa){        this.sampleFileld=sa;    }}public class AccessibleObjectDemo {    public static void main(String [] args) throws NoSuchMethodException {        AccessibleObject sampleMethod = SampClass.class.getMethod("sampleMethod");            System.out.println("sampleMethod.isAnnotationPresent:"+sampleMethod.isAnnotationPresent(Cus.class));        //輸出結果：sampleMethod.isAnnotationPresent:true    }}

getAnnotations()樣本：

@Retention(RetentionPolicy.RUNTIME)@interface Tt{    public String name();    public String value();}@Tt(name = "SampleClass",value = "Sample Class Annotation")class SampClass2{    private String sampleFileld;    @Tt(name = "sampleMethod",value = "sample Method Annotation")    public String sampleMethod(){        return "sample";    }    public String getSampleFileld(){        return sampleFileld;    }    public void setSampleFileld(String sa){        this.sampleFileld=sa;    }}public class AccessibleObjectDemo2 {    public static void main(String [] args) throws NoSuchMethodException {        AccessibleObject sampleMethod = SampClass2.class.getMethod("sampleMethod");        Annotation[] annotations = sampleMethod.getAnnotations();        for(int i=0;i<annotations.length;i++){            if(annotations[i] instanceof Tt){                Tt cus2= (Tt) annotations[i];                System.out.println(cus2.name());                System.out.println(cus2.value());                /*                輸出結果：                 sampleMethod                  sample Method Annotation                * */            }        }    }}

 

java基礎源碼 (4)--reflect包-AnnotatedElement介面