java - 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 Debug模式下获取了嵌套类的类类型，但无法创建实例来在下一步中初始化嵌套实例的字段。 (请参阅我的评论行)。所以我的单元测试因错误而失败。

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，虽然您为容器类 Nested 创建实例，但您没有为封闭类 FirstNested 和 SecondNested 创建实例。为了制作这些实例，您可以像这样更改您的类

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，您必须实现(可能以递归方式)创建新实例并将这些实例注册到您的容器类实例。

类似这样的事情

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

或者你可以保持类不变并使用类似的东西

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可以在这里找到 How to instantiate inner class with reflection in Java?