Downcasting and Run-Time Type Identification (RTTI) : class cast « Class « Java

1. Java
2. Class
3. class cast

Downcasting and Run-Time Type Identification (RTTI)

// : c07:RTTI.java
// Downcasting & Run-Time Type Identification (RTTI).
// {ThrowsException}
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.

class Useful {
  public void f() {
  }

  public void g() {
  }
}

class MoreUseful extends Useful {
  public void f() {
  }

  public void g() {
  }

  public void u() {
  }

  public void v() {
  }

  public void w() {
  }
}

public class RTTI {
  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/RTTI
    ((MoreUseful) x[0]).u(); // Exception thrown
  }
} ///:~


           
       

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