我无法创建嵌套类的实例，也无法初始化字段。 我想通过单元测试

Question

我在调试模式下获得了嵌套类的类类型，但是无法创建实例以在下一步中初始化嵌套实例的字段。 （请参见我的文章）。 所以我的单元测试失败并显示错误。

public class Reflector {
public static <T> T initialize(Class<? extends T> clazz) {

    try {
        Object classInstance = clazz.newInstance();
        System.out.println("MainclassInstance: "+ classInstance.toString());

        for (Field field : clazz.getDeclaredFields()) {

            System.out.println(
             "\n### 1. For-Schleife\nclazz.getDeclaredFields().size(): " + clazz.getDeclaredFields().length);

            System.out.println("clazz.field: " + field.getName());

            //Class Object
            if (field.getType().isMemberClass()) {

                Object memberClassInstance = field.getType();      //Nested$FirstNested

                System.out.println("memberClassInstance: " + memberClassInstance.toString()); //Nested$FirstNested

                List<Field> memberClassFields = Arrays.asList(((Class<?>) memberClassInstance).getDeclaredFields());

                for (int memberFieldIndex = 0; memberFieldIndex < memberClassFields.size() - 1; memberFieldIndex++) {
                    System.out.println("meberClassField: " + memberClassFields.get(memberFieldIndex).getName());


                    //memberClassFields.get(memberFieldIndex).set(memberClassInstance, "nestedField");
                }
                //field.set(memberClassInstance, "MyObject");
                //field.set(classInstance, memberClassInstance);
            }

        }

        return (T) classInstance;

    } catch (SecurityException | IllegalArgumentException e) {
        e.printStackTrace();
    } catch (InstantiationException ex) {
        Logger.getLogger(Reflector.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        Logger.getLogger(Reflector.class.getName()).log(Level.SEVERE, null, ex);
    }

    return null;
}

这是JUnit测试类

public class ReflectorTest {

    @Test
    public void testInitializeNestedObject() {
        Nested actual = Reflector.initialize(Nested.class);

        assertNotNull(actual);
        assertNotNull(actual.nested1);
        assertTrue(actual.nested1 instanceof Nested.FirstNested);
        assertNotNull(actual.nested1.nestedField1);
        assertNotNull(actual.nested1.nestedField2);

        assertNotNull(actual.nested2);
        assertTrue(actual.nested2 instanceof Nested.SecondNested);
        assertNotNull(actual.nested2.nestedField3);
        assertNotNull(actual.nested2.nestedField4);
    }
}

这是数据类

public class Nested {

    public class FirstNested{
        public Object nestedField1;
        public Object nestedField2;
    }

    public class SecondNested{
        public Object nestedField3;
        public Object nestedField4;
    }

    public FirstNested nested1;
    public SecondNested nested2;

}

Answer 1

问题是，尽管为容器类Nested创建了实例，但没有为封闭的类FirstNested和SecondNested创建实例。 为了创建此类实例，您可以像这样更改类

public static class Nested
{
    public static class FirstNested
    {
        public Object nestedField1;
        public Object nestedField2;
    }

    public static class SecondNested
    {
        public Object nestedField3;
        public Object nestedField4;
    }

    public FirstNested nested1;
    public SecondNested nested2;

}

您必须将内部类设为静态，以便可以通过反射轻松访问它们。 然后，您必须（可能以递归的方式）实现新实例的创建并将这些实例注册到您的容器类实例。

像这样

Object memberClassInstance = field.getType().newInstance();
field.set(classInstance, memberClassInstance);

或者，您可以按原样保留类并使用类似的内容

Object memberClassInstance = field.getType().getConstructor(Nested.class).newInstance()

正如@CoronA在评论中提到的。 有关如何实例化内部类的更多信息，请参见此处。 如何在Java中使用反射实例化内部类？

Answer 2

正确的解决方案：

public class Reflector {
public static <T> T initialize(Class<? extends T> clazz) {

    try {
        Object classInstance = clazz.newInstance();
        System.out.println("MainclassInstance: " + classInstance.toString());

        for (Field field : clazz.getDeclaredFields()) {

            System.out.println(
                    "\n### 1. For-Schleife\nclazz.getDeclaredFields().size(): "
                    + clazz.getDeclaredFields().length);

            System.out.println("clazz.field: " + field.getName());


            //Class Object
            if (field.getType().isMemberClass()) {


                Object innerInstance = null;
                try {

                    Class<?> innerClass = Class.forName(field.getType().getName());
                    Constructor<?> ctor = innerClass.getDeclaredConstructor(classInstance.getClass());
                    innerInstance = ctor.newInstance(classInstance);
                } catch (InvocationTargetException ex) {
                    Logger.getLogger(Reflector.class.getName()).log(Level.SEVERE, null, ex);
                } catch (ClassNotFoundException ex) {
                    Logger.getLogger(Reflector.class.getName()).log(Level.SEVERE, null, ex);
                } catch (NoSuchMethodException ex) {
                    Logger.getLogger(Reflector.class.getName()).log(Level.SEVERE, null, ex);
                }

                //###############
                Object memberClassInstance = field.getType();      //Nested$FirstNested

                System.out.println("memberClassInstance: " + memberClassInstance.toString()); //Nested$FirstNested

                List<Field> memberClassFields = Arrays.asList((innerInstance.getClass()).getDeclaredFields());

                for (int memberFieldIndex = 0; memberFieldIndex < memberClassFields.size() - 1; memberFieldIndex++) {
                    System.out.println("meberClassField: " + memberClassFields.get(memberFieldIndex).getName());
                    memberClassFields.get(memberFieldIndex).set(innerInstance, memberClassFields.get(memberFieldIndex).getName() + (memberFieldIndex+1));     
                }

                field.set(classInstance,innerInstance);

            }

        }

        return (T) classInstance;

    } catch (SecurityException | IllegalArgumentException e) {
        e.printStackTrace();
    } catch (InstantiationException ex) {
        Logger.getLogger(Reflector.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        Logger.getLogger(Reflector.class.getName()).log(Level.SEVERE, null, ex);
    }

    return null;
}