java反多态的代码_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

packageTest0817;importjava.lang.reflect.InvocationTargetException;importjava.lang.reflect.Method;classBase{inta;

Base(){

a=1;

System.out.println("Base Construct");

}public voidf(){

System.out.println("Base");

}

}class Sub extendsBase{inta;intb;

Sub(){

a=2;

b=2;

System.out.println("Sub Construct");

}

Sub(inti){

a=i;

b=i;

System.out.println("Sub Construct.this have one param");

}public voidf(){

System.out.println("Sub");

}public void f(intm){

System.out.println("Sub,the m = "+m);

}

}public classTestFanshe {public static void main(String[] args) throwsInstantiationException, 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();

}

}

}

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