Java 中的类 getAnnotationsByType()方法，带示例

原文:https://www . geeksforgeeks . org/class-getannotationsbytype-method-in-Java-with-examples/

java.lang.Class 类 的 getAnnotationsByType() 方法用于获取该类中存在的指定标注类型的标注。方法返回指定批注类型的批注数组。

语法:

public A[] getAnnotationsByType(Class<T> annotationClass)

参数:该方法接受一个参数标注类，即要获取的标注类型。

返回值:该方法返回指定标注类型的标注数组。

异常:如果给定的注释类为空，该方法抛出:

  • [null pointer exception: .

下面的程序演示了 getAnnotationsByType()方法。

例 1:

// Java program to demonstrate
// getAnnotationsByType() method

import java.util.*;
import java.lang.annotation.*;

// create a custom Annotation
@Retention(RetentionPolicy.RUNTIME)
@interface Annotation {

    // This annotation has two attributes.
    public String key();

    public String value();
}

// call Annotation for method
// and pass values for annotation
@Annotation(key = "GFG", value = "GeeksForGeeks")
public class Test {

    public Object obj;

    public static void main(String[] args)
        throws ClassNotFoundException
    {

        // returns the Class object for this class
        Class myClass = Test.class;

        System.out.println(
            "Class represented by myClass: "
            + myClass.toString());

        // Get the annotation
        // using getAnnotationsByType() method
        System.out.println(
            "Annotation of myClass of type Annotation: "
            + Arrays.toString(
                  myClass
                      .getAnnotationsByType(
                          Annotation.class)));
    }
}

输出:

Class represented by myClass: class Test
Annotation of myClass of type Annotation: [@Annotation(key=GFG, value=GeeksForGeeks)]

例 2:

// Java program to demonstrate
// getAnnotationsByType() method

import java.util.*;
import java.lang.annotation.*;

@Deprecated
public class Test {

    public Object obj;

    public static void main(String[] args)
        throws ClassNotFoundException
    {
        try {
            // returns the Class object for this class
            Class myClass = Test.class;

            System.out.println(
                "Class represented by myClass: "
                + myClass.toString());

            // Get the annotation
            // using getAnnotationsByType() method
            System.out.println(
                "Annotation of myClass of type Deprecated: "
                + Arrays.toString(
                      myClass
                          .getAnnotationsByType(
                              Deprecated.class)));
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

输出:

Class represented by myClass: class Test
Annotation of myClass of type Deprecated: [@java.lang.Deprecated()]

参考:https://docs . Oracle . com/javase/9/docs/API/Java/lang/class . html # getannocationsbytype-Java . lang . class-

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