Code demonstration of Java reflection and polymorphism (parent class calling subclass)

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 has 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"); The full package name is required. Class name
Sub s = (sub) c.newinstance ();//instantiation
Get the constructor function
C.getconstructors ();
Get the method
method = C.getmethod ("f");
System.out.println ("The Method is" +method.tostring ());

class[] Paramerclass = new Class[1];
Paramerclass[0] = Int.class; This place is going to write int, which is consistent with the parameter type of the formal parameter, and the method cannot be found by writing an integer.
Method method1 = C.getmethod ("f", Paramerclass);
System.out.println ("The Method is" +method1.tostring ());
Method of invoking the S object through reflection
Method.invoke (s); Parameter-free

int a=10;
Method1.invoke (S, a); of a parameter
Method1.invoke (S, 20);

Instantiation, pointing to the parent class reference
Base B = (base) c.newinstance ();
Base bs = (Sub) c.newinstance ();
Sub sb = (Base) c.newinstance (); Error
S.F (); Output Sub
B.f (); Output Sub
B.F (10);//error, unable to invoke child class method not in parent class
BS.F (); Output Sub
BS.F (10);//error, unable to invoke child class method not in parent class
} catch (ClassNotFoundException e) {
System.out.println ("No such exception occurs");
E.printstacktrace ();
}catch (Nosuchmethodexception e) {
System.out.println ("No such method exception occurred");
E.printstacktrace ();
}catch (IllegalArgumentException e) {
TODO auto-generated Catch block
E.printstacktrace ();
} catch (InvocationTargetException e) {
TODO auto-generated Catch block
E.printstacktrace ();
}

}

}

Output Result:

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"); }}classSubextendsbase{intA; intb; Sub () {a=2; b=2; System.out.println ("Sub Construct"); } Sub (inti) {a=i; b=i; System.out.println ("Sub Construct.this has one param"); }     Public voidf () {System.out.println ("Sub"); }     Public voidFintm) {System.out.println ("Sub,the m =" +m); }} Public classTestfanshe { Public Static voidMain (string[] args)throwsinstantiationexception, Illegalaccessexception, SecurityException {Class<?>C; Try{C= Class.forName ("Test0817.sub");//the full package name is required. class nameSub s = (sub) c.newinstance ();//instantiation of//get the constructor functionc.getconstructors (); //Get the methodmethod = C.getmethod ("F"); System.out.println ("The method is" +method.tostring ()); Class[] Paramerclass=NewClass[1]; paramerclass[0] =int.class;//This place is going to write int, which is consistent with the parameter type of the formal parameter, and the method cannot be found by writing an integer .Method method1 = C.getmethod ("F", Paramerclass); System.out.println ("The method is" +method1.tostring ()); //method of invoking the S object through reflectionMethod.invoke (s);//parameter-free                        inta=10; Method1.invoke (S, a); //of a parameterMethod1.invoke (S, 20); //instantiation, pointing to the parent class referenceBase B =(Base) c.newinstance (); Base BS=(Sub) c.newinstance (); //Sub sb = (Base) c.newinstance (); ErrorS.F ();//Output SubB.f ();//Output Sub//B.f (ten);//error, unable to call child class method not in parent classBS.F ();//Output Sub//BS.F (ten);//error, unable to call child class method not in parent class}Catch(ClassNotFoundException e) {System.out.println ("No such exception occurred");        E.printstacktrace (); }Catch(nosuchmethodexception e) {System.out.println ("No This method exception occurred");        E.printstacktrace (); }Catch(IllegalArgumentException e) {//TODO auto-generated Catch blockE.printstacktrace (); } Catch(InvocationTargetException e) {//TODO auto-generated Catch blockE.printstacktrace (); }            }}

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Code demonstration of Java reflection and polymorphism (parent class calling subclass)