java 方法类| Java 中的 getParameterAnnotations()方法

方法类| Java 中的 getParameterAnnotations()方法

原文:https://www . geesforgeks . org/method-class-get parameter annotations-method-in-Java/

方法类的方法返回一个二维注释数组，代表方法对象的参数注释。如果方法不包含参数，将返回一个空数组。如果该方法包含一个或多个参数，则将返回一个二维注释数组。对于没有注释的参数，此二维数组的嵌套数组将为空。

在编译时，强制和合成参数被添加到数组中。强制参数是在源中隐式声明的参数，合成参数是在源中既不隐式也不显式声明的参数。

此方法返回的注释对象是可序列化的。此方法返回的数组可以很容易地修改。

语法:

public Annotation[][] getParameterAnnotations()

返回值:该方法返回一个二维注释数组，表示方法对象的形式参数和隐式参数的注释。

下面的程序说明了方法类的 getParameterAnnotations()方法:

示例 1: 对作为输入给定的特定方法使用 getParameterAnnotations()。

该程序包含一个方法名 setManyValues()，其中包含参数注释。所以这个程序将获取 setManyValues()方法包含的所有参数注释。

// Java program to demonstrate how to
// apply getParameterAnnotations() method
// of Method Class.

import java.lang.annotation.Annotation;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Method;

public class GFG {

    // Main method
    public static void main(String[] args)
    {
        try {
            // create class object
            Class classobj = GFG.class;

            // create method object of setManyValues
            Method setManyValueObject = null;

            Method[] methods = classobj.getMethods();

            for (Method m : methods) {
                if (m.getName().equals("setManyValues"))
                    setManyValueObject = m;
            }

            // get Annotation of parameter
            Annotation[][] Arrayannotations = setManyValueObject
                                                  .getParameterAnnotations();

            System.out.println("Method Name: "
                               + setManyValueObject.getName());

            // print parameter annotation
            for (Annotation[] annotationRow : Arrayannotations) {
                for (Annotation annotation : annotationRow) {
                    AnnotationDemo anndemo = (AnnotationDemo)annotation;
                    System.out.println("key of annotation: "
                                       + anndemo.key());
                    System.out.println("value of annotation: "
                                       + anndemo.value());
                }
            }
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }

    // method name setManyValues
    public void
        setManyValues(@AnnotationDemo(key = "methodParameter1",
                                      value = "Some value")
                      String parameter1)
    {
        System.out.println("setManyValues");
    }
}

// create a custom Annotation to apply on method
@Retention(RetentionPolicy.RUNTIME)
@interface AnnotationDemo {

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

    public String value();
}

输出:

Method Name: setManyValues
key of annotation: methodParameter1
value of annotation: Some value

示例 2: 如果方法包含 ParameterAnnotations，则对 GFG 类的方法使用 getParameterAnnotations()。

// Java program to demonstrate how to
// apply getParameterAnnotations() method
// of Method Class.

import java.lang.annotation.Annotation;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Method;

public class GFG {

    // Main method
    public static void main(String[] args)
    {
        try {
            // create class object
            Class classobj = GFG.class;

            // create list of method objects
            Method[] methods = classobj.getMethods();

            for (Method m : methods) {

                // print details for only getValues
                // and setValue method
                // so filter list of methods
                if (m.getName().equals("getValues")
                    || m.getName().equals("setValue")) {

                    // get Annotations of parameter
                    Annotation[][] Arrayannotations
                        = m
                              .getParameterAnnotations();

                    System.out.println("Method Name: "
                                       + m.getName());

                    // print parameter annotation
                    printAnnotation(Arrayannotations);
                }
            }
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }

    // method name setValue with
    // no annotations at parameter
    public void setValue()
    {
        System.out.println("setValue");
    }

    // method name getValues with annotations at the parameter
    public String
        getValues(@AnnotationDemo(field1 = "GFG",
                                  field2 = "Works",
                                  field3 = "fine",
                                  field4 = "Hurray!!")
                  String value)
    {
        System.out.println("setManyValues");
        return value;
    }

    public static void
        printAnnotation(Annotation[][] Arrayannotations)
    {
        System.out.println("Annotation length: "
                           + Arrayannotations.length);

        // print parameter annotation
        for (Annotation[] annotationRow : Arrayannotations) {
            for (Annotation annotation : annotationRow) {

                AnnotationDemo anndemo = (AnnotationDemo)annotation;
                System.out.println("field1 of annotation: "
                                   + anndemo.field1());
                System.out.println("field2 of annotation: "
                                   + anndemo.field2());
                System.out.println("field3 of annotation: "
                                   + anndemo.field3());
                System.out.println("field4 of annotation: "
                                   + anndemo.field4());
            }
        }
    }
}

// create a custom Annotation to apply on method
@Retention(RetentionPolicy.RUNTIME)
@interface AnnotationDemo {

    // This annotation has many attributes.
    public String field1();
    public String field2();
    public String field3();
    public String field4();
}

输出:

Method Name: getValues
Annotation length: 1
field1 of annotation: GFG
field2 of annotation: Works
field3 of annotation: fine
field4 of annotation: Hurray!!
Method Name: setValue
Annotation length: 0