OnJava8-Examples/polymorphism/Reflect.java at master · CSapprenticeWT/OnJava8-Examples · GitHub

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// polymorphism/Reflect.java

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

// {ThrowsException}

class Useful {

public void f() {}

public void g() {}

}

class MoreUseful extends Useful {

@Override public void f() {}

@Override public void g() {}

public void u() {}

public void v() {}

public void w() {}

}

public class Reflect {

public static void main(String[] args) {

Useful[] x = {

new Useful(),

new MoreUseful()

};

x[0].f();

x[1].g();

// Compile time: method not found in Useful:

//- x[1].u();

((MoreUseful)x[1]).u(); // Downcast/Reflect

((MoreUseful)x[0]).u(); // Exception thrown

}

/* Output:

___[ Error Output ]___

Exception in thread "main"

java.lang.ClassCastException: Useful cannot be cast to

MoreUseful

at Reflect.main(Reflect.java:28)