Java中的反射

获取反射的类

//获取反射的类
    public static void printReflectionClass() throws Exception {
        Fruit fruit = new Fruit();
        Class<?> class1 = fruit.getClass();
        System.out.println(class1);
        Class<?> class2 = Fruit.class;
        System.out.println(class2);
        Class<?> class3 = Class.forName("com.golearning.learning.bean.Fruit");
        System.out.println(class3);
    }

运行结果：
class com.golearning.learning.bean.Fruit
class com.golearning.learning.bean.Fruit
class com.golearning.learning.bean.Fruit

获取一下传入的类的属性和类型

    /**
     * 获取一下传入的类的属性和类型
     * @param cla
     */
    public static void getRefClassField(Class<?> cla){
        Field[] fields = cla.getDeclaredFields();
        for (Field field : fields) {
            System.out.println(field.getName()+" = "+field.getType());
        }

    }

        Class<?> cla = Class.forName("com.golearning.learning.bean.Fruit");
        getRefClassField(cla);

运行结果为：
size = int
color = class java.lang.String
shape = class java.lang.String

获取一下传入的类里面的方法

    /**
     * 获取一下传入的类里面的方法
     * @param cla
     */
    public static void getRefClassMethod(Class<?> cla) throws NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
        Method[] methods = cla.getDeclaredMethods();
        for (Method method : methods) {
            //获取方法的名字和有参参数个数数
            System.out.println(method.getName() + " == 参数个数 == "+method.getParameterCount());
            //获取方法的参数类型
            Class[] classes = method.getParameterTypes();
            for (Class aClass : classes) {
                System.out.println(aClass);
            }
        }
        //执行反射获取到的方法
        Method method1 = cla.getDeclaredMethod("setColor",String.class);
        Object object = cla.newInstance();
        method1.invoke(object,"红色");
        System.out.println(object);

    }

给一个泛型List 插入一条非泛型的数据

    /**
     * 给一个泛型List 插入一条非泛型的数据
     * @param list
     * @throws NoSuchMethodException
     * @throws InvocationTargetException
     * @throws IllegalAccessException
     */
    public static void addDataInGenericList(List<String> list) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        //获取它的类
        Class<?> cla = list.getClass();
        //获取它的add方法 参数为任意对象
        Method method = cla.getDeclaredMethod("add",Object.class);
        method.invoke(list,514);
        for (Object o : list) {
            System.out.println(o);
        }
    }

        List<String> list = new ArrayList<>();
        list.add("爷爷今年有");
        list.add("99了");
        //给一个泛型List 插入一条非泛型的数据
        addDataInGenericList(list);

运行结果：
爷爷今年有
99了
514

获取传入类的构造器创建对象

public class Fruit {
    //大小
    private Integer size;
    //颜色
    private String color;
    //形状
    private String shape;

    public Fruit(Integer size, String color, String shape) {
        System.out.println("=====================获取有参构造器===================");
        this.size = size;
        this.color = color;
        this.shape = shape;
    }

    public Fruit() {
        System.out.println("=====================获取无参构造器===================");
    }

    public int getSize() {
        return size;
    }

    public void setSize(Integer size) {
        this.size = size;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getShape() {
        return shape;
    }

    public void setShape(String shape) {
        this.shape = shape;
    }

    @Override
    public String toString() {
        return "Fruit{" +
                "size=" + size +
                ", color='" + color + '\'' +
                ", shape='" + shape + '\'' +
                '}';
    }
}

    /**
     * 获取传入类的构造器创建对象
     * @param cla
     */
    public static void getRefClassConstractor(Class<?> cla) throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
       //获取无参构造器
        Constructor<?> constructor =  cla.getConstructor(null);
        Object object = constructor.newInstance(null);
        System.out.println(object);
        //获取有参构造器
        Constructor<?> constructor2 =  cla.getConstructor(Integer.class,String.class,String.class);
        Object object2 = constructor2.newInstance(40,"红色","圆形");
        System.out.println(object2);
    }

          Class<?> cla = Class.forName("com.golearning.learning.bean.Fruit");
          getRefClassConstractor(cla);

运行结果为：
=====================获取无参构造器===================
Fruit{size=null, color='null', shape='null'}
=====================获取有参构造器===================
Fruit{size=40, color='红色', shape='圆形'}

注解的反射

在一个类中使用注解

//多个属性之间要用逗号隔开，赋值方式在括号内以value = ""的方式。
@AnnotationClass(height = 11,shape = "ddd",deep = 45)
public class Plants {
    private int height;
    private String shape;
    private int deep;
    private int width;

    public Plants(int height, String shape, int deep, int width) {
        this.height = height;
        this.shape = shape;
        this.deep = deep;
        this.width = width;
    }

    public Plants() {
    }

    public int getHeight() {
        return height;
    }

    public void setHeight(int height) {
        this.height = height;
    }

    public String getShape() {
        return shape;
    }

    public void setShape(String shape) {
        this.shape = shape;
    }

    public int getDeep() {
        return deep;
    }

    public void setDeep(int deep) {
        this.deep = deep;
    }

    public int getWidth() {
        return width;
    }

    public void setWidth(int width) {
        this.width = width;
    }

    @Override
    public String toString() {
        return "Plants{" +
                "height=" + height +
                ", shape='" + shape + '\'' +
                ", deep=" + deep +
                ", width=" + width +
                '}';
    }
}

定义一个注解

@Target(ElementType.TYPE) //表示AnnotationClass注解可以用于什么地方，可用于给一个类型进行注解，比如类、接口、枚举
@Retention(RetentionPolicy.RUNTIME)//表示AnnotationClass注解传递存活时间，注解可保留到程序运行时被加载到JVM中
public @interface AnnotationClass
{
    //Integer heightx();//不能使用封装类型
    int height();//参数的类型只能是基本类型
    String shape();
    int deep();
    int width() default 10;

}

获取传入类的注解属性

    /**
     * 获取传入类的注解属性
     * @param cla
     */
    public static void getAnnotationInfo(Class cla){
        AnnotationClass annotationClass = (AnnotationClass) cla.getAnnotation(AnnotationClass.class);
        if(annotationClass!=null){
            System.out.println("deep=="+annotationClass.deep());
            System.out.println("height=="+annotationClass.height());
            System.out.println("shape=="+annotationClass.shape());
            System.out.println("width=="+annotationClass.width());
        }
    }