反射类之调用运行时类中指定的结构：属性、方法、构造器

调用运行时类中指定的结构：属性、方法、构造器

一，测试用例

Creature类

public class Creature<T> implements Serializable {

    private char gender;
    public double weight;

    private void breath(){
        System.out.println("生物呼吸");
    }

    public void eat(){
        System.out.println("吃东西");
    }
}

Person类

@MyAnnotation(value = "hi")
public class Person extends Creature<String> implements Comparable<String>, MyInterface{

    private  String name;
    int age;
    public int id;
    public Person(){

    }
    @MyAnnotation(value = "ac")
    private Person(String name){
        this.name = name;
    }
    @MyAnnotation
    Person(String name, int age){
        this.name = name;
        this.age = age;
    }
    @MyAnnotation(value = "asda asd")
    private String show(String nation){
        System.out.println("我的国籍是：" + nation);
        return nation;
    }

    public String display(String interests , int age) throws NullPointerException,ClassCastException{
        return interests + age;
    }

    @Override
    public void info() {
        System.out.println("I am people");
    }

    @Override
    public int compareTo(String o) {
        return 0;
    }

    private static void showDesc(){
        System.out.println("我是一个可爱的人");
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", id=" + id +
                '}';
    }
}

MyAnnotation注解类

@Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE, MODULE})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
    String value() default "hello";
}

MyInterface接口类

public interface MyInterface {
    void info();
}

二，反射测试

/*
        不需要掌握
     */
    @Test
    public void testField() throws Exception {
        Class clazz = Person.class;

        //创建运行时类的对象
        Person p = (Person) clazz.newInstance();
        //获取指定的属性：要求运行时类中属性声明为public
        //通常不采用此方法
        Field id = clazz.getField("id");

        /*
        设置当前属性的值
        set():参数1：指明设置哪个对象的属性   参数2：将此属性值设置为多少
         */
        id.set(p,1001);

        /*
        获取当前属性的值
        get():参数1：获取哪个对象的当前属性值
         */
        int pid = (int) id.get(p);
        System.out.println(pid);
    }

    /*
    如何操作运行时类中的指定的属性 -- 需要掌握
     */
    @Test
    public void testField1() throws IllegalAccessException, InstantiationException, NoSuchFieldException {
        Class clazz = Person.class;

        //创建运行时类的对象
        Person p = (Person) clazz.newInstance();
        //1. getDeclaredField(String fieldName):获取运行时类中指定变量名的属性
        Field name = clazz.getDeclaredField("name");

        //2.保证当前属性是可访问的
        name.setAccessible(true);//IllegalAccessException(非法访问)
        //3.获取、设置指定对象的此属性值
        name.set(p,"Tom");

        System.out.println(name.get(p));
    }

    /*
    如何操作运行时类中的指定的方法 -- 需要掌握
     */
    @Test
    public void testMethod() throws IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
        Class clazz = Person.class;

        //创建运行时类的对象
        Person p = (Person) clazz.newInstance();

        /*
        1.获取指定的某个方法
        getDeclaredMethod():参数1 ：指明获取的方法的名称  参数2：指明获取的方法的形参列表
         */
        Method show = clazz.getDeclaredMethod("show", String.class);

        //2.保证当前方法是可访问的
        show.setAccessible(true);

        /*
        3. 调用方法的invoke():参数1：方法的调用者  参数2：给方法形参赋值的实参
        invoke()的返回值即为对应类中调用的方法的返回值。
         */
        Object chn = show.invoke(p, "CHN");

        System.out.println(chn);

        System.out.println("*************如何调用静态方法*****************");

        // private static void showDesc()
        Method showDesc = clazz.getDeclaredMethod("showDesc");
        showDesc.setAccessible(true);
        //如果调用的运行时类中的方法没有返回值，则此invoke()返回null
//        Object returnVal = showDesc.invoke(null);
        Object invoke = showDesc.invoke(Person.class);
        System.out.println(invoke);//null
    }

    /*
    如何调用运行时类中的指定的构造器
     */
    @Test
    public void testConstruction() throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        Class clazz = Person.class;

        //private Person(String name)
        /*
        1.获取指定的构造器
        getDeclaredConstructor():参数：指明构造器的参数列表
         */
        Constructor declaredConstructor = clazz.getDeclaredConstructor(String.class);

        //2.保证此构造器是可访问的
        declaredConstructor.setAccessible(true);

        //3.调用此构造器创建运行时类的对象
        Person per = (Person) declaredConstructor.newInstance("Tom");
        System.out.println(per);


    }

三，获取当前运行时类的属性结构

 @Test
    public void test1(){
        Class clazz = Person.class;

        //获取属性结构
        //getFields():获取当前运行时类及其父类中声明为public访问权限的属性
        Field[] fields = clazz.getFields();
        for (Field field : fields) {
            System.out.println(field);
        }
        System.out.println();

        //getDeclaredFields():获取当前运行时类中声明的所有属性。（不包含父类中声明的属性）
        Field[] declaredFields = clazz.getDeclaredFields();
        for (Field declaredField : declaredFields) {
            System.out.println(declaredField);
        }
    }


    //权限修饰符  数据类型 变量名
    @Test
    public void test2(){
        Class clazz = Person.class;
        Field[] declaredFields = clazz.getDeclaredFields();
        for (Field declaredField : declaredFields) {
            //1.权限修饰符
            int modifiers = declaredField.getModifiers();
            System.out.print(Modifier.toString(modifiers) + "\t");
            //2.数据类型
//            declaredField.getType()
            Type genericType = declaredField.getGenericType();
            System.out.print(genericType + "\t");
            //3.变量名
            String name = declaredField.getName();
            System.out.println(name);
            System.out.println();
        }
    }

四，获取运行时类的方法结构

@Test
public void test1(){
    Class clazz = Person.class;

    //getMethods():获取当前运行时类及其所有父类中声明为public权限的方法
    Method[] methods = clazz.getMethods();
    for (Method method : methods) {
        System.out.println(method);
    }
    System.out.println();

    //getDeclaredMethods():获取当前运行时类中声明的所有方法。（不包含父类中声明的方法）
    Method[] declaredMethods = clazz.getDeclaredMethods();
    for (Method declaredMethod : declaredMethods) {
        System.out.println(declaredMethod);
    }
}

/*
@Xxxx
权限修饰符  返回值类型  方法名(参数类型1 形参名1,...) throws XxxException{}
 */
@Test
public void test2(){
    Class clazz = Person.class;
    Method[] declaredMethods = clazz.getDeclaredMethods();
    for (Method declaredMethod : declaredMethods) {
        //1.获取方法声明的注解
        Annotation[] annotations = declaredMethod.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        //2.权限修饰符
        System.out.print(Modifier.toString(declaredMethod.getModifiers()) + "\t");

        //3.返回值类型
        System.out.print(declaredMethod.getReturnType().getName() + "\t");

        //4.方法名
        System.out.print(declaredMethod.getName());
        System.out.print("(");

        //5.形参列表
        Class[] parameterTypes = declaredMethod.getParameterTypes();
        if(!(parameterTypes == null && parameterTypes.length == 0)){
            for(int i = 0;i < parameterTypes.length;i++){

                if(i == parameterTypes.length - 1){
                    System.out.print(parameterTypes[i].getName() + " args_" + i);
                    break;
                }
                System.out.print(parameterTypes[i].getName() + " args_" + i + ",");
            }
        }

        System.out.print(")");

        //6.抛出的异常
        Class[] exceptionTypes = declaredMethod.getExceptionTypes();
        if(exceptionTypes.length > 0){
            System.out.print("throws ");
            for(int i = 0;i < exceptionTypes.length;i++){
                if(i == exceptionTypes.length - 1){
                    System.out.print(exceptionTypes[i].getName());
                    break;
                }

                System.out.print(exceptionTypes[i].getName() + ",");
            }
        }
        System.out.println();
    }
}

五，

/*
    获取构造器结构
     */
    @Test
    public void test1(){
       Class clazz = Person.class;

        //getConstructors():获取当前运行时类中声明为public的构造器
        Constructor[] constructors = clazz.getConstructors();
        for (Constructor constructor : constructors) {
            System.out.println(constructor);
        }
        System.out.println();

        //getDeclaredConstructors():获取当前运行时类中声明的所有的构造器
        Constructor[] declaredConstructors = clazz.getDeclaredConstructors();
        for (Constructor declaredConstructor : declaredConstructors) {
            System.out.println(declaredConstructor);
        }
    }

    /*
    获取运行时类的父类
     */
    @Test
    public void test2(){
        Class clazz = Person.class;

        Class superclass = clazz.getSuperclass();
        System.out.println(superclass);
    }

    /*
    获取运行时类的带泛型的父类

     */
    @Test
    public void test3(){
        Class clazz = Person.class;

        Type genericSuperclass = clazz.getGenericSuperclass();
        System.out.println(genericSuperclass);
    }

    /*
    获取运行时类的带泛型的父类的泛型

    代码：逻辑性代码  vs 功能性代码
     */
    @Test
    public void test4(){
        Class clazz = Person.class;

        Type genericSuperclass = clazz.getGenericSuperclass();
        ParameterizedType paramType = (ParameterizedType) genericSuperclass;

        //获取泛型类型
        Type[] actualTypeArguments = paramType.getActualTypeArguments();
//        System.out.println(actualTypeArguments[0].getTypeName());
        System.out.println(((Class) actualTypeArguments[0]).getName());
    }

    /*
    获取运行时类实现的接口
     */
    @Test
    public void test5(){
        Class clazz = Person.class;
        Class[] interfaces = clazz.getInterfaces();
        for (Class anInterface : interfaces) {
            System.out.println(anInterface);
        }

        System.out.println();

        //获取运行时类的父类实现的接口
        Class[] interfaces1 = clazz.getSuperclass().getInterfaces();
        for (Class aClass : interfaces1) {
            System.out.println(aClass);
        }
    }

    /*
        获取运行时类所在的包
     */
    @Test
    public void test6(){
        Class clazz = Person.class;

        Package aPackage = clazz.getPackage();
        System.out.println(aPackage);
    }

    /*
        获取运行时类声明的注解
     */
    @Test
    public void test7(){
        Class clazz = Person.class;

        Annotation[] annotations = clazz.getAnnotations();
        for(Annotation annos : annotations){
            System.out.println(annos);
        }
    }