java反射与多态（父类调用子类）的代码演示

package Test0817;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

class Base{
int a;

Base(){
a=1;
System.out.println("Base Construct");
}
public void f(){
System.out.println("Base");
}
}

class Sub extends Base{
int a;
int b;
Sub(){
a=2;
b=2;
System.out.println("Sub Construct");
}

Sub(int i){
a=i;
b=i;
System.out.println("Sub Construct.this have one param");
}
public void f(){
System.out.println("Sub");
}
public void f(int m){
System.out.println("Sub,the m = "+m);
}
}

public class TestFanshe {

public static void main(String[] args) throws InstantiationException, IllegalAccessException, SecurityException {
Class<?> c;
try {
c = Class.forName("Test0817.Sub"); //需要有完整的包名.类名
Sub s = (Sub) c.newInstance();//实例化
//得到构造函数
c.getConstructors();
//得到方法
Method method = c.getMethod("f");
System.out.println("the method is "+method.toString());

Class[] paramerClass = new Class[1];
paramerClass[0] = int.class; //这个地方要写int,与形参的参数类型一致，写Integer就会报方法找不到
Method method1 = c.getMethod("f", paramerClass);
System.out.println("the method is "+method1.toString());
//通过反射，调用s对象的方法
method.invoke(s); //无参数的

int a=10;
method1.invoke(s, a); //一个参数的
method1.invoke(s, 20);

//实例化，将父类引用指向
Base b = (Base) c.newInstance();
Base bs = (Sub) c.newInstance();
//Sub sb = (Base) c.newInstance(); 报错
s.f(); //输出 sub
b.f(); //输出 sub
//b.f(10);//报错，无法调用父类中没有的子类方法
bs.f(); //输出 sub
//bs.f(10);//报错，无法调用父类中没有的子类方法
} catch (ClassNotFoundException e) {
System.out.println("发生无该类异常");
e.printStackTrace();
}catch(NoSuchMethodException e){
System.out.println("发生无该方法异常");
e.printStackTrace();
}catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

}

输出结果：

Base Construct
Sub Construct
the method is public void Test0817.Sub.f()
the method is public void Test0817.Sub.f(int)
Sub
Sub,the m = 10
Sub,the m = 20
Base Construct
Sub Construct
Base Construct
Sub Construct

package Test0817;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

class Base{
    int a;

    Base(){
        a=1;
        System.out.println("Base Construct");
    }
    public void f(){
        System.out.println("Base");
    }
}

class Sub extends Base{
    int a;
    int b;
    Sub(){
        a=2;
        b=2;
        System.out.println("Sub Construct");
    }

    Sub(int i){
        a=i;
        b=i;
        System.out.println("Sub Construct.this have one param");
    }
    public void f(){
        System.out.println("Sub");
    }
    public void f(int m){
        System.out.println("Sub,the m = "+m);
    }
}

public class TestFanshe {

    public static void main(String[] args) throws InstantiationException, IllegalAccessException, SecurityException {
        Class<?> c;
        try {
            c = Class.forName("Test0817.Sub"); //需要有完整的包名.类名
            Sub s = (Sub) c.newInstance();//实例化
            //得到构造函数
            c.getConstructors();
            //得到方法
            Method method = c.getMethod("f");
            System.out.println("the method is "+method.toString());

            Class[] paramerClass = new Class[1];
            paramerClass[0] = int.class; //这个地方要写int,与形参的参数类型一致，写Integer就会报方法找不到
            Method method1 = c.getMethod("f", paramerClass);
            System.out.println("the method is "+method1.toString());
            //通过反射，调用s对象的方法
            method.invoke(s); //无参数的

            int a=10;
            method1.invoke(s, a); //一个参数的
            method1.invoke(s, 20);

            //实例化，将父类引用指向
            Base b = (Base) c.newInstance();
            Base bs = (Sub) c.newInstance();
            //Sub sb = (Base) c.newInstance(); 报错
            s.f(); //输出 sub
            b.f(); //输出 sub
            //b.f(10);//报错，无法调用父类中没有的子类方法
            bs.f(); //输出 sub
            //bs.f(10);//报错，无法调用父类中没有的子类方法
        } catch (ClassNotFoundException e) {
            System.out.println("发生无该类异常");
            e.printStackTrace();
        }catch(NoSuchMethodException e){
            System.out.println("发生无该方法异常");
            e.printStackTrace();
        }catch (IllegalArgumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

}